"Mark my words," Donald Trump said when he launched his presidential campaign on June 16, 2015.

Trump had just promised to "build a great wall," on the U.S.-Mexico border, "very inexpensively."

"And I will have Mexico pay for that wall," he said.

More than three years into Trump's presidency, his administration's actions have not risen to his promise.

Trump's administration mainly replaced barriers installed by previous administrations with new ones that are expected to be more effective in stopping illegal immigration and drug smuggling. Mexico has not paid for any construction. Americans are paying the costs

The U.S.-Mexico border spans approximately 2,000 miles, and about a third of it has barriers raised by the U.S government over decades. That hasn't increased during Trump's presidency.

Some sections of the border have up to three layers of barriers that run parallel to the border. The first impediment a migrant heading to the United States may face is known by officials as the primary barrier — fencing to stop people on foot and in vehicles. Secondary barriers, located behind the primary, are in place to stop pedestrians. (A third layer, or tertiary fence, is primarily used to delineate property lines rather than to deter illegal entries, said a 2017 report from the U.S. Government Accountability Office.)

When Trump was campaigning to become president, the southwest border had 654 miles of primary barriers. Under Trump, that has increased by three miles, to 657.

What else? As of late June, 184 miles of dilapidated primary barriers were replaced with updated fences. Twelve miles that had dilapidated secondary barriers now have new structures. And secondary barriers were raised for the first time along 17 miles.

U.S. Customs and Border Protection over the years has used bollard, wire mesh, and chain link style fencing as barriers. "Landing mat" fencing — built using Vietnam War-era helicopter landing mats — has also been used. The new barriers going up include 18- to 30-foot high steel bollard fences.

The Trump administration says it's built a new "border wall system" — steel-bollard fences, all-weather roads, lighting, cameras and other surveillance technology.

The barriers constructed are very different from the pedestrian and vehicle fencing that they are replacing, said a January report from the Congressional Research Service. They pose "a formidable barrier, but it is not the high, thick masonry structure that most dictionaries term a 'wall'," the report said.

Overall, when Trump says they've built 200 miles or more of border wall, what he's referring to is the replacement of older barriers with new fences, not 200 miles of barriers protecting the border for the first time.

It's not a wall, but it's not nothing.

"Replacing vehicle barriers with the bollard-style pedestrian barriers may not represent new miles of primary barriers along the border, but it does represent a new obstacle that changes the calculus of those attempting to cross the border between ports of entry," the Congressional Research Service report said.

Trump gave different answers during his 2016 campaign when asked about the cost of building a border wall. At times he said $8 billion, or $12 billion.

Customs and Border Protection in June told PolitiFact that the administration had identified approximately $15 billion to construct more than 700 miles of new "border wall system." (That mileage includes projects completed, and about 400 of the 700 miles are replacement projects.)

The Mexican government is not one of the funding sources. The money would come from the U.S. departments of Homeland Security and Defense, and from the Treasury Forfeiture Fund.

Trump has largely failed to get Congress to appropriate funds to speed up construction. Congress has appropriated $4.47 billion for border barrier planning and construction: about $1.04 billion specifically for barrier replacement projects, about $1.41 without specifying whether funding was for barrier replacements, and about $2.02 billion specifically for construction needs in the Rio Grande Valley sector.

Another obstacle Trump has faced comes from landowners in Texas who are putting up a legal fight against the administration's intent to obtain their private land for border barrier construction. Given the current pace of construction, ongoing court battles related to the Defense Department funding and land needed for construction, the Trump administration will not complete a total 700 miles by the end of 2020

Trump did not campaign saying he would improve or reinforce existing barriers, and that's mainly what he's done. When Trump said he would build a wall, he gave the impression that he would barricade parts of the border that were not protected. The work that's been completed doesn't reflect his campaign rhetoric. Mexico also hasn't paid for the construction.

Trump did not fulfill his promise to build a wall and make Mexico pay for it. We rate this a Promise Broken.

President Donald Trump remains committed to building a border wall with Mexico, but he hasn't been able to get the money to do it. And Mexico doesn't seem poised to pay for it, either.

The federal government is in a partial shutdown because Trump says he won't sign any spending bill that doesn't include $5.7 billion to build the wall. Democrats in Congress are unwilling to vote for a bill providing that money.

Even though Trump is demanding billions for the wall from U.S. taxpayers, he's also contending that the wall will be paid for through a renegotiated trade deal that hasn't yet cleared U.S. Congress. It also needs final legislative approval from Mexico and Canada, the two other countries party to the agreement.

Trade experts have pushed back against Trump's false claims that the renegotiated North American Free Trade Agreement (renamed by Trump as the United States-Mexico-Canada Agreement) will pay for the wall. Trump claims that the United States will see added revenue from the potential deal. But even if U.S. tax revenue increases in response to increased revenues of U.S. firms, Congress would still need to allocate that money for the wall. Trump so far has failed to secure that wall money from Congress.

The Trump administration earlier received about $1.6 billion from Congress for border barriers. But that money wasn't used to build any new wall. Conditions for the money said it could only be for designs previously used, such as fencing.

As the government is in a partial shutdown over Trump's demand for money for the border wall, he's said that the wall doesn't have to be concrete, that it could be a barrier of steel slats. But he's also said that a concrete option remains. Several factors remain unknown: whether Trump and Congress will agree on funding for a border wall, how much that funding would be, and what kind of wall would be built.

As matters stand, Mexico has not paid for a wall. Congress has not appropriated money for a wall. Fencing is being built or has been completed at the southwest border. But not a wall.

Trump's promise to build a border wall and have Mexico pay for it has not been fulfilled, and the government is in shutdown as the fight continues. We rate this as Stalled.

President Donald Trump has secured $1.57 billion for barriers along the southwest border — advancing his promise to secure the border but falling significantly short of his desired $25 billion for a wall.

"We funded the initial down payment of $1.6 billion," Trump said March 23 after signing a $1.3 trillion omnibus spending bill into law. "We are going to be starting work literally on Monday on not only on some new wall, not enough, but we are working on that very quickly. But also fixing existing walls and existing acceptable fences."

The funds, however, won't be used to construct any of the wall prototypes standing in California near the U.S.-Mexico border, which Trump toured earlier this month.

The designated funds, the bill said, "shall only be available for operationally effective designs deployed as of the date of the Consolidated Appropriations Act, 2017, (Public Law 115–31), such as currently deployed steel bollard designs, that prioritize agent safety." U.S. Customs and Border Protection told PolitiFact on March 13, 2018, that the wall prototypes were still being evaluated.

The bill Trump signed specifically called for:

• $251 million for approximately 14 miles of secondary fencing along the southwest border in the San Diego sector;

• $445 million for 25 miles of primary pedestrian levee fencing along the southwest border in the Rio Grande Valley Sector;

• $196 million for primary pedestrian fencing along the southwest border in the Rio Grande Valley Sector;

• $445 million for replacement of existing primary pedestrian fencing along the southwest border;

• $38 million for border barrier planning and design; and

• $196 million for acquisition and deployment of border security technology

Earlier in the day, Trump threatened to veto the bill because it did not fully fund his long-promised border wall.

"I am considering a VETO of the Omnibus Spending Bill based on the fact that the 800,000 plus DACA recipients have been totally abandoned by the Democrats (not even mentioned in Bill) and the BORDER WALL, which is desperately needed for our National Defense, is not fully funded," Trump tweeted.

Trump described the $1.6 billion as "a short-term funding." The funds will be used to secure the border through fencing. It's still unclear which wall prototype will be used for the wall, which Mexico still says it's not paying for, despite Trump's promise.

For now, we continue to rate Trump's promise to build a wall and make Mexico pay for it as In the Works.

Donald Trump supporters chanted "build the wall" at his rallies, as he promised them an impenetrable, physical, tall and beautiful wall with Mexico. Not a fence.

But since the election, Trump has said parts of the wall will actually be see-through and that the barrier could also consist of fencing. His administration also seeks taxpayer money to cover the costs, though he pledged Mexico would pay for it.

Despite his post-election remarks and comments from his own staff, Trump claims that he plans to deliver what he promised.

"The Wall is the Wall, it has never changed or evolved from the first day I conceived of it. Parts will be, of necessity, see through and it was never intended to be built in areas where there is natural protection such as mountains, wastelands or tough rivers or water....." he tweeted.

Trump also maintained that Mexico would pay for it — but did not offer concrete details on how or a clear timeframe — as he asked Congress for $18 billion.

"The Wall will be paid for, directly or indirectly, or through longer term reimbursement, by Mexico, which has a ridiculous $71 billion dollar trade surplus with the U.S. The $20 billion dollar Wall is 'peanuts' compared to what Mexico makes from the U.S. NAFTA is a bad joke!" Trump tweeted.

(We've noted that the trade deficit has nothing to do with whether the Mexican government could afford to pay the wall.)

Trump gave varying figures for the cost of the wall during the campaign, from $8 billion to $12 billion.

But The Wall Street Journal reported on Jan. 5 that his administration outlined to a group of senators plans requesting nearly $18 billion to build new and replacement barriers along more than 700 miles of the nearly 2,000-mile long U.S.-Mexico border.

The administration's document called for a barrier, referred to as a "wall system," but officials did not specify where it would be constructed, The Wall Street Journal reported. Trump's administration asked for $9.3 billion over the first five years and $8.7 billion over the next five years, the newspaper reported.

U.S. Customs and Border Protection would not confirm to PolitiFact the details reported by The Wall Street Journal, and the White House did not respond to requests for information.

At an immigration meeting between Trump and a group of bipartisan lawmakers on Jan. 9, Democratic Sen. Mazie K. Hirono, of Hawaii, asked Trump if it was still his position that he wanted $18 billion for a wall or there would be no deal for young immigrants who came to the United States as children and are now at risk of deportation.

"Yeah. I can build it for less, by the way," Trump responded.

The $18 billion for the border barrier is part of a $33 billion package, which also requests $5.7 billion for towers, surveillance equipment and other technology; $1 billion for road construction and maintenance; and $8.5 billion for border security personnel, according to The Wall Street Journal.

A CBP spokesman told PolitiFact officials are still testing and evaluating wall prototypes built in California.

It's unclear if lawmakers will approve Trump's request for border barriers. A taxpayer-funded border wall would be a departure from Trump's repeated promises of Mexico covering the costs.

Pending appropriations and construction, Trump's border wall promise remains In the Works.

Construction of eight border wall prototypes is under way as the Department of Homeland Security seeks to advance President Donald Trump's landmark promise.

The construction includes four concrete wall prototypes and four prototypes using "other materials." Construction began Sept. 26 in San Diego, Calif., close to the U.S.-Mexico border. The prototypes are expected to be finished near the end of October.

The prototypes will be designed to deter illegal immigration in the area where they are constructed and be between 18 to 30 feet high, U.S. Customs and Border Protection said in a Sept. 26 news release.

"Moving forward with the prototypes enables us to continue to incorporate all the tools necessary to secure our border," Ronald Vitiello, CBP acting deputy commissioner, said in the news release.

In an August press conference announcing contracts awarded for concrete prototypes, Vitiello said officials will examine the prototypes' aesthetics, how penetrable and resistant they are to tampering, and their anti-scaling or anti-climb features. Those contracts ranged from just under $400,000 to just under $500,000.

"There's still a lot to do, right. We are going to build four prototypes for concrete and then we are going to build four other materials, and then we are going to make decisions about which is most appropriate for which location," Vitiello said.

Evaluation of prototypes will take 30 to 60 days, he said.

Congress approved $20 million to start wall planning and to award for the construction of the prototypes, CBP spokesman Roger Maier told PolitiFact.

Companies building concrete border wall prototypes include the following:

• Caddell Construction Co., (DE), LLC, Montgomery, Ala.

• Fisher Sand & Gravel Co., DBA Fisher Industries, Tempe, Ariz.

• Texas Sterling Construction Co., Houston

• W. G. Yates & Sons Construction Co., Philadelphia, Miss.

Companies building border wall prototypes with other materials:

• Caddell Construction Co., (DE), LLC, Montgomery, Ala.

• KWR Construction, Inc., Sierra Vista, Ariz.

• ELTA North America Inc., Annapolis Junction, Md.

• W. G. Yates & Sons Construction Co., Philadelphia, Miss.

It remains uncertain where funding will come from for a more extensive border wall. Mexico continues to say it will not pay the costs, and Democrats in Congress have also resisted funding the construction.

Still, with the prototypes' construction, the Trump administration is moving forward on the promise. For now, we continue to rate Trump's pledge In the Works.

Is President Donald Trump ready to compromise on his plan to make Mexico pay for a border wall? During an Aug. 22 rally in Phoenix, Trump brought up the wall many times but did not say that Mexico will pay for it, as he had repeatedly done on the campaign trail.

He did say one thing new to our ears: He threatened a government shutdown if "obstructionist Democrats" try to prevent the wall from being built.

"And we are building a wall on the southern border, which is absolutely necessary," Trump said. "Now the obstructionist Democrats would like us not to do it. But believe me, if we have to close down our government, we're building that wall."

One possible source of funding is making its way through Congress.

The House of Representatives on July 27 passed a $790 billion funding bill (H.R. 3219) that includes $1.6 billion for 28 miles of new levee wall and 46 miles of fencing along the U.S.-Mexico border. Congress and the White House must agree on a funding plan before Sept. 30, the start of the next fiscal year.

Trump's threat to shut down the government comes a few weeks after a leaked transcript of a phone call between Trump and Mexican President Pena Nieto showed the two leaders butting heads over which country would foot the bill.

During the Jan. 27 conversation, Trump asked Nieto to stop saying publicly that Mexico will not pay for the wall because it put Trump in a political bind.

Another detail of his promise, the type of wall, has changed over the past several months. Trump said during the campaign that the wall would be "impenetrable." In July he said it would be a "steel wall with openings." He has also brought up the idea of creating a wall with solar panels.

At the Phoenix rally, Trump said he's aiming to build "walls that you can see through in a sense. You want to see what's on the other side."

H.R. 3219 specifies funding for 32 miles of "bollard fencing," 28 miles of "bollard levee wall," and 14 miles of "secondary fencing." A bollard is an upright steel post.

But before any type of border walls or fences are built, the funding bill still needs Senate approval. We continue to rate this promise In the Works.

A House committee has given preliminary approval to about $1.6 billion for 28 miles of a new levee wall along the U.S.-Mexico border and 46 miles of fencing.

The money for border infrastructure construction includes:

• 28 miles of new levee wall in the Rio Grande Valley, at $498 million;

• 32 miles of new border fencing in the Rio Grande Valley, at $784 million; and,

• 14 miles of secondary fencing in San Diego, Calif., at $251 million

The House Appropriations Committee on July 18 voted 30-22 on a proposed bill to provide the Department of Homeland Security with $44.3 billion in discretionary funding for the fiscal year beginning Oct. 1, 2017, and ending Sept. 30, 2018.

The proposed funding is in addition to money appropriated in fiscal year 2017 for the replacement of 40 miles of primary fencing in sectors of California and Texas ($15 million for 2 miles in El Centro, Calif.; $102 million for 14 miles in San Diego, Calif.; and $175 million for 24 miles in El Paso, Texas).

The Associated Press reported that Republican leaders plan to attach funding for border security to a spending bill for the Defense Department and other agencies. The House is expected to consider that spending bill soon.

Details on the length and type of wall remain uncertain. In March, U.S. Customs and Border Protection began accepting proposals for the design and construction of wall prototypes — solid concrete and other types. In late June, DHS told the New York Times prototype constructions would begin this summer but did not specify when exactly.

At a June 21 rally in Iowa, Trump told supporters he had come up with the idea for a solar wall that would pay for itself.

Trump during the campaign said the wall would be "impenetrable." But on July 12, he said the wall could be "a steel wall with openings" because being able to see through to the other side was necessary.

"And I'll give you an example. As horrible as it sounds, when they throw the large sacks of drugs over, and if you have people on the other side of the wall, you don't see them, they hit you on the head with 60 pounds of stuff? It's over. As crazy as that sounds, you need transparency through that wall," Trump said.

Trump also said that the nearly 2,000-mile border only needed a wall for sections totalling 700 to 900 miles, because natural barriers and remote areas already deterred illegal crossings in those sectors.

Part of Trump's border wall promise is that Mexico will pay for the costs — but Mexico still rejects that idea, and Trump has not offered more details on how that will be achieved.

While the House Appropriations Committee approved the funding, those funds still need full congressional approval. DHS also plans to construct wall prototypes this summer, but there's a long way to go before Trump's "big, beautiful wall" is completed. We continue to rate Trump's border wall promise In the Works.

President Donald Trump is asking Congress for $44.1 billion for the Department of Homeland Security for fiscal year 2018, including $1.6 billion to secure 74 miles along the U.S.-Mexico border. 

The requested $1.6 billion would cover: 

• 32 miles of new border wall construction along the Rio Grande Valley sector;

• 28 miles of new levee wall along the Rio Grande Valley sector; and,

• 14 miles of new border wall to replace existing secondary fence in the San Diego sector. 

Fiscal year 2018 runs from Oct. 1, 2017 to Sept. 30, 2018.

Homeland Security officials said on May 23 they are doing a sector-by-sector border analysis and getting feedback from Border Patrol to identify the areas of most need. 

DHS Secretary John Kelly told Congress on April 5 that it's "unlikely that we will build a wall or physical barrier from sea to shining sea," but that he's committed to putting it up in areas recommended by agents on the ground.

In some parts of the nearly 2,000-mile U.S.-Mexico border, building a concrete wall may be problematic due to rough terrain conditions.

 "The president knows that I'm looking at every variation on the theme and I have no doubt when I go back to him and say, 'You know, boss, wall makes sense here, fencing -- high-tech fencing -- makes sense over here, technology makes sense over here,' I have no doubt that he will go tell me to do it," Kelly told a Senate committee in April.

It's up to Congress whether Trump will get the requested border security funding for fiscal year 2018. In the meantime, his promise to build a wall and make Mexico pay for it remains In the Works.

Department of Homeland Security John Kelly issued a memo Feb. 20 directing an agency within his department, U.S. Customs and Border Protection, to move forward on Trump's executive order to build a wall along the southern border.

"Consistent with the president's executive order, the will of Congress and the need to secure the border in the national interest, CBP, in consultation with the appropriate executive departments and agencies, and nongovernmental entities having relevant expertise -- and using materials originating in the United States to the maximum extent permitted by law -- shall immediately begin planning, design, construction and maintenance of a wall," the memo said.

Kelly's memo also called for the use of technology, patrol and access roads to gain operational control of the border.

Kelly directed the Under Secretary for Management and CBP commissioner to allocate all sources of available funding for the planning, design, construction and maintenance of the wall and for other security measures. They were also instructed to develop project-specific congressional budget requests for the current and subsequent fiscal years.

In a Q&A posted on DHS website, the department says it has identified locations near El Paso, Texas; Tucson, Ariz.; and El Centro, Calif., for wall construction because "fence or old brittle landing-mat fencing are no longer effective."

Border Patrol is also assessing priority areas where a wall or similar physical barriers can be built, the department said.

New DHS information advances Trump's promise to build a wall along the U.S.-Mexico border. Pending wall construction, we continue to rate this promise In the Works.

President Donald Trump has signed an executive order to push forward one of his biggest campaign promises: build a wall along the border with Mexico.

The executive order signed Jan. 25, five days after Trump's inauguration, instructs departments and agencies to "deploy all lawful means" to secure the southern border, prevent further illegal immigration and to send immigrants in the country illegally back to their countries.

The order sets forth Trump's policy to secure the border "through the immediate construction of a physical wall," to prevent drug trafficking and terrorism.

It directs the secretary of homeland security to:

"In accordance with existing law, including the Secure Fence Act and IIRIRA, take all appropriate steps to immediately plan, design, and construct a physical wall along the southern border, using appropriate materials and technology to most effectively achieve complete operational control of the southern border."

The order defines "wall" as "a contiguous, physical wall or other similarly secure, contiguous, and impassable physical barrier."

It also asks the department to identify and allocate sources of federal funds for the planning, design, and construction of the physical wall, and to prepare congressional budget requests for the current and upcoming fiscal years.

In an interview with ABC News' David Muir aired Jan. 25, Trump said wall construction would start in months.

At a press briefing, Trump's press secretary Sean Spicer said plans for the wall will kick off with funding already available, and that Trump will work with Congress for additional funding.

"There are a lot of funding mechanisms that can be used," Spicer said. "At this point, his goal was to get the project started as quickly as possible using existing funds and resources that the department currently has, and then to move forward and work with Congress on an appropriation schedule."

Spicer also affirmed the president's plan to have Mexico pay back for the wall, saying it would happen "one way or another."

"A nation without borders is not a nation. Beginning today, the United States of America gets back control of its borders, gets back its borders," Trump said Jan. 25 at the Department of Homeland Security.

On Jan. 23, Mexican President Enrique Peña Nieto issued 10 objectives his government will seek in negotiations with the United States, among them opposition to a wall. "While Mexico recognizes the rights of every sovereign nation to guarantee its security, Mexico does not believe in walls," Peña Nieto said.

There are 702 miles of fencing along the nearly 2,000-mile U.S.-Mexico border. The fencing includes 652 miles of primary fencing, 36 miles of secondary fencing and 14 miles of tertiary fencing, according to U.S. Customs and Border Protection.

"If Congress acts to fund the construction of Trump's border wall and spares no expense, then it could be done very quickly," said Alex Nowrasteh, an immigration expert at the libertarian Cato Institute. "However, previous government attempts to build fences were behind schedule and over budget."

Other experts have told us it could take years to build a border wall.

Trump's pledge is to build a wall and have Mexico cover the costs. While Trump is moving forward on his promise, the wall is yet to be built and Mexico has not provided funds. We rate this promise, In the Works.

One of Donald Trump's signature promises is to build a wall along the border with Mexico. He's said it will be big, powerful, tall, beautiful, impenetrable.

"I would build a great wall, and nobody builds walls better than me, believe me, and I'll build them very inexpensively," Trump said June 16, 2015, when he launched his campaign for the White House. "I will build a great, great wall on our southern border. And I will have Mexico pay for that wall."

"Build the wall!" chants became a staple at his campaign events. But there's a lot at play, from getting a foreign sovereign nation to foot the bill to sorting out the specifics of this monumental endeavor.

WHY HE'S PROMISING IT

Trump says stronger border security, particularly a wall, will end illegal immigration and cut the flow of illicit drugs pouring into the United States.

The U.S.-Mexico border stretches nearly 2,000 miles, more than half of it along the Colorado River and Rio Grande. By May 2015, there were about 650 miles of vehicle and pedestrian fencing, according to a March 2016 report from the U.S. Government Accountability Office.

WHAT NEEDS TO HAPPEN

For Trump to carry out his real estate promise, he'll need funding from Congress and/or Mexico's money. He's outlined potential regulatory changes that he believes will persuade Mexico to comply.

Trump's team has said Congress could appropriate funds for the construction of the wall "to make it more speedy, and then having Mexico pay for it after the fact."

To get Mexico to pay for it, Trump has said he would introduce rules so that no immigrant would be able to send money outside the United States unless they show documentation proving their legal status. He would do that by  changing rules that regulate money transfer companies and wire transfers.

Trump says Mexico receives an estimated $24 billion a year in remittances from people in the United States and assumes Mexico will protest U.S. attempts to bar undocumented immigrants from sending money to Mexico.

Trump has said a rule modifying definitions of financial institutions and accounts would not go into effect if Mexico makes a one-time payment of $5 billion to $10 billion, which would go toward border security.

HOW MUCH WILL IT COST

Trump's estimates of the wall's price varied throughout the campaign, at times saying $8 billion or $12 billion. He hasn't been decisive about its physical form, either, suggesting it could rise 35 to 40 feet, or 50 feet, or higher.

But he's said a wall doesn't need to run the nearly 2,000 mile border, but only half of that "because we have natural barriers."

Without precise plans, it's hard to determine how much it would cost to build the wall. By some estimates, completing fencing along the border may cost at least $5.1 billion. Others have estimated that securing the remaining approximate 1,300 miles along the border could cost as much as $25 billion.

WHAT'S STANDING IN HIS WAY

If Trump plans to have Mexico refund him the cost of building the wall, then he faces opposition from Mexican President Enrique Peña Nieto, who has said there's "no way" his country would pay for the wall. (Peña Nieto's 6-year term ends in 2018.)

Engineering and immigration experts have told PolitiFact that the federal government would need to acquire private land along the border and compensate owners for it through eminent domain. That process could take years if landowners put up a fight.

"Every piece of land is different," Paul Barkhurst, an eminent domain litigation lawyer based in San Antonio told PolitiFact Texas back in February 2016. "You're talking about a massive project across many, many states. It just depends on how much resources they want to put on it."

A POSSIBLE TIMELINE

Once the wall's specifics are determined, there's a planning period that could go on for at least one year (including terrain surveying and finalization of design issues), plus project bidding, experts say. Environmental impact studies may also be commissioned.

Engineering experts believe it would take years to build a wall, though it's hard to tell exactly how many without detailed specifics. It's also undetermined when and if Mexico would pay for the wall.