The promise: In the 2008 election, Barack Obama pledged to create secure borders. He said that would mean "additional personnel, infrastructure and technology on the border and at our ports of entry."

Four years later, do we have secure borders?

To adequately answer that question, we would need to know what percentage of people who try to enter the country illegally get caught.

Unfortunately for politicos who love clarity, all we have are imperfect measures.

"We don't really know the denominator," said Louis DeSipio, a political scientist who researches immigration at the University of California, Irvine.

In other words, we know how many we catch, but we don't know if that's most, half, or just a sliver of the total number of people crossing illegally.

Here's what we do know:

- The number of people we're catching as they try to cross the border illegally has decreased dramatically.

- The number of people we're removing per year is at an all-time high.

- Following a trend initiated by Presidents Bill Clinton and George W. Bush, the Obama administration has added more border patrol agents, fencing and detection technology to prevent border crossings.

- Two years ago, slightly less than half the Southwest Border met Homeland Security's border security standard of under "operational control."

- Changes in enforcement have had an effect on reduced illegal immigration, but not all the credit should go to policymakers: The down economy in the U.S., especially in the housing sector, played a major role in the decline.

Last year the number of apprehensions near the border (340,000) was the lowest since 1971. That's in contrast to slightly more than 1 million apprehensions, the number in 2005.

Apprehensions correlate closely with illegal immigration patterns, said Jeffrey Passel, a demographer with the Pew Hispanic Center.

As apprehensions go down, one should expect that illegal immigration would go down as well.

A word of caution though: It's really a measure of how many people Border Patrol catches, not how many people attempt to cross. Imagine two scenarios:

Scenario 1: Fewer people from Mexico try to cross the Southwest border, so Border Patrol reports fewer people caught.

Scenario 2: Border Patrol cuts back on staff, changes reporting procedures, or begins using detection technology that malfunctions frequently -- and fails to catch some people who cross. Apprehensions go down, but illegal immigration does not.

Thus it's conceivable the current apprehensions trend is misleading.

In this case though, "every other measure tells you is that immigration is on the decline," said Gordon Hanson, an economist who researches immigration at the University of California, San Diego. "We've got a whole bunch of imperfect measures and they all tell a similar story."

For instance, the number of removals in 2009 and 2010 were higher than in any year under Bush or Clinton. The reason removals matter in a discussion about illegal immigration? Because many people actually enter the country on a legal visa, but stay after it expires.

The number of illegal immigrants in the U.S. declined from a peak of about 12 million in 2007 to about 11.1 million in 2009. Since then, the number has remained relatively flat, said Passel, the demographer.

Homeland Security's "operational control" measure is the strongest evidence touted by groups who favor stricter immigration controls and say the borders aren't secure.

We spoke with Mark Krikorian, executive director of Center for Immigration Studies, who referenced a 2010 report on border security by the Government Accountability Office, a nonpartisan analytical arm of Congress.

The report says that 44 percent of the 2,000-mile Southwest border is under "operational control," a term that represents the level of borders security provided through the number of border patrol agents, fencing and detection technology, such as heat sensors and drones.

Another 37 percent of the border is monitored, with a high chance of detecting crossings, but Border Patrol isn't able to respond because of obstacles such as lack of transportation access or difficult terrain. The report also mentions that the percentage under "operational control" had been increasing by an average of 126 miles per year between 2005 and 2010.

"I don't think it has much scientific merit," said Hanson, the economist. "It's a measure of investment. It's not a measure of return on investment."

Valid or not, the most recent figure we have on "operational control" is two years old because Homeland Security scrapped the measure in favor of a new index that the department said would debut in 2012. It hasn't yet.

Some Republicans are tired of waiting for the new measure. Rep. Candice Miller, R-Mich., introduced a bill in June calling for Homeland Security to reinstate its "operational control" reporting.

Krikorian said his definition of secure borders would -- at the very least -- mean a Southwest border 100 percent under "operational control."

"Secure borders" probably does not mean no illegal immigration though. Even in a scenario where the country marshalled all its resources to border security, it's plausible that people would still find a way to cross.

Edward Alden, an immigration researcher at the Council on Foreign Relations, a nonpartisan think tank, said that even in the Cold War-era when East Germany tried to keep its residents from escaping to West Germany, there were still people who managed to cross.

"You cannot imagine a scenario where it would be impossible to cross the border," Alden said.

We also think it's worth noting that even though Obama's subject heading for the promise was "create secure borders," his specific, measurable pledges were about investing in additional staffing and resources.  

As we reported last year, personnel and other resources to stop illegal crossings of the U.S.-Mexico border have increased dramatically in recent years. One vivid statistic from Homeland Security: The number of border patrol officers more than doubled from about 10,000 to about 21,000 between 2004 and 2012.

In our last update on this campaign promise, we warned that it's difficult to parse the effect of increased enforcement from the effect of changing economic conditions. Hanson, who has run statistical models to estimate factors that explain changes in illegal immigration, says the two biggest factors are enforcement and the economy, and they are equal in weight. In the case of the economy, the U.S. recession and the slowdown of home construction -- which employed many illegal immigrants -- is closely associated with less people trying to immigrate to the U.S.

Without a clear-cut definition on what "secure borders" means, it's difficult to grade Obama on his performance. Many signs point to significant progress on stemming illegal immigration, including added staff and resources in border security. But reports have indicated that a sizeable portion of the border is not under "operational control." We rate this promise a Compromise.

With President Barack Obama giving a major speech on immigration in El Paso, we thought it would be a good time to check on his promise to secure the borders. We last examined this promise in July 2010 and found that Obama had provided additional support on border security, but evidence was mixed on whether illegal border crossings declined.

In March 2011, the U.S. Government Accountability Office released a report, "Border Security: DHS Progress and Challenges in Securing the U.S. Southwest and Northern Borders," in conjunction with testimony from GAO Director Richard Stana.

The report confirmed that personnel and other resources to stop illegal crossings of the U.S.-Mexico border have increased dramatically in recent years. In 2004, the U.S. Department of Homeland Security was created, reorganizing several federal agencies under a single roof. That year, the agency had 10,500 agents to patrol land borders; 17,600 agents for air, land and sea ports of entry; and a budget of $5.9 billion. At the end of fiscal year 2010, almost 20,000 agents patrolled land borders; 20,600 agents monitored ports of entry; and the budget amounted to $11.9 billion.

So there are more resources being sent to the border. But have they been effective?

U.S. Customs and Border Protection has reported apprehensions nationwide decreased by 36 percent between 2008 and 2010, from nearly 724,000 apprehensions to 463,000. The border patrol credited that to fewer people attempting to illegally cross the border because of beefed up enforcement.

Two experts we spoke with had more nuanced views.

They warned that the depressed U.S. economy has led to lower levels of immigration.

"There still is a large undocumented population of roughly 11 million, a decrease from the 12 million when the president took office," said Kevin Johnson, dean of the University of California-Davis Law School and an immigration policy expert, via e-mail. "The decrease might be attributable some to increased enforcement but also is attributable to the economy and the lack of jobs during the recession."

Louis DeSipio of the University of California-Irvine, cautioned us that about half of illegal immigrants in the U.S. entered on short-term visas and then simply stayed. "Border enforcement does little to slow this flow," he said via e-mail.

He added that he was "not yet convinced" that more enforcement at the border is reducing illegal immigration: "I think that the real test will be when the U.S. economy recovers, particularly the sectors that employed a high share of unauthorized immigrants in the last decade: construction, hospitality, light manufacturing, and household maintenance."

We'll give the Obama administration credit for increased resources at the border, but we're not yet ready to render a final verdict on this promise. We leave the rating In the Works.

Immigration reform was a major component of President Obama's campaign platform. He promised to secure the border, crack down on employers who hire undocumented immigrants, and provide a path to citizenship for undocumented immigrants.

We reviewed the first promise in that list back in March 2009. At the time, we rated it In the Works, since the administration had announced that it was beefing up security on the border with Mexico. We wanted to see if there has been any movement on the promise since then.

The White House made our job a bit easier with a June 21, 2010 entry in its blog, which summarizes some of the major initiatives and accomplishments of the President's border security policy. It notes that the number of personnel assigned to Border Enforcement Security Task Forces has doubled over the past year and that the number of ICE intelligence analysts along the Southwest border has tripled. Thirteen additional cross-trained canine teams were also deployed to the region, according to the report.

President Obama also announced in May 2010 that he would deploy 1,200 national guard troops to help secure the border. Of those troops, 524 will be stationed in Arizona, which has made national headlines in recent months for its new immigration law, which Gov. Brewer signed back in April.

We contacted numerous border security experts and immigration groups to see what they thought of President Obama's border security programs.

"The efforts are a significant continuation of a more than 15 year effort to beef up the southwest border of the United States," said David Shirk, Director of the Trans-Border Institute at University of San Diego. Most of the other experts that we spoke with agreed. But Louis DeSipio from the University of California-Irvine called the policies "incremental," and argued that "the Obama efforts aren't dramatically different than the late Bush efforts." The one possible exception, DeSipio said, is the increased focus on the monitoring of southbound cargo. DeSipio said that increased focus was a partly a result of "growing complaints from Mexico about firearms going south".

We also wondered whether the new measures were effective at curbing illegal border crossings.

"Although opinions may differ, I do not see any of the immigration enforcement changes pursued by the Obama administration as having a long term impact on the undocumented immigrant population," Kevin Johnson, Dean of the University of California-Davis Law School and an immigration policy expert, wrote in an email. "Where the administration's enforcement efforts might prove to be -- but have not yet proven to be -- 'significant' is if they help convince members of Congress that the border is secure and it is time to reform the laws. Both Presidents Bush and Obama believed that they must appear willing to enforce the immigration laws to secure immigration reform. President Bush failed and President Obama has so far."

Just to be thorough, we also checked to see what's being done to beef up security on the U.S.-Canada border. We spoke with Christopher Sands, a U.S.-Canada relations expert at the Hudson Institute, a public policy think tank.

"Overall, I think that the Obama administration is doing well securing the US-Canadian border. They have continued the Bush administration's agenda of upgrading old and inadequate infrastructure, maintained the trusted traveler and shipper programs to keep trade flowing, taken advantage of technology -- particularly for remote areas-- and fostered close ties with Canadian customs, law enforcement and intelligence agencies," said Sands.

Still, the programs have their share of critics. Sen. John McCain, R-Ariz., said that it would take 3,000 additional troops to secure Arizona alone. He proposed sending 6,000 National Guard troops to the border. Arizona Governor Jan Brewer is also pushing for more troops, along with seeking reimbursement for the state's cost of incarcerating illegal immigrants.

We initially considered rating this one Promise Kept, since the promise was to provide "additional personnel, infrastructure and technology on the border and at our ports of entry". Our research shows that Obama's accomplished that. Still, you'd expect additional security to make a meaningful dent in illegal border crossings and violence. The experts we spoke with told us that they've yet to see that happen. So for now, we're keeping this one In the Works.

This is one of the more vague promises in our database. It comes from an Obama campaign fact sheet on immigration that offered broad language but few details.

And because it's so vague, it's a relatively easy one for Obama to fulfill. He didn't commit to a specific amount of money or promise to implement a particular program. He merely said he would "support additional personnel, infrastructure and technology on the border and at our ports of entry."

A rash of violence involving Mexican drug cartels prompted the administration to announce March 24, 2009, that it would beef up security on the border with Mexico. Homeland Security Secretary Janet Napolitano said the administration would be spending $700 million to help the Mexican government track the activities of the drug cartels. The money will be used for new communications gear, five helicopters and a surveillance aircraft for the Mexican navy.

The White House said the Department of Homeland Security was also tripling the number of intelligence analysts working along the Southwest border, bolstering the use of biometric identification, increasing the scrutiny of trains, and "enhanced use of technology at ports of entry," including more use of mobile X-ray systems that can see through trucks and shipping containers.

The sweeping program is targeted to combat Mexican drug violence, but it fulfills Obama's promise because the original pledge was so vague. Still, it's so targeted at the drug cartels that we'd like to see the administration's broader initiatives for border security before we make this one a Promise Kept. So for now, we rate it In the Works.