The government is spending more than ever before to crack down on illegal immigration, but the bang for the taxpayer buck has plummeted.

The Obama administration allocated $17.9 billion last year to the three agencies in charge of policing our borders—substantially more than it devoted for the combined budgets of the FBI, Secret Service, Drug Enforcement Administration, the U.S. Marshals Service, and the Bureau of Alcohol, Tobacco, Firearms and Explosives. Over the past seven years, the Department of Homeland Security doubled the number of agents patrolling the border to 21,444.

Yet apprehensions of illegal immigrants dropped to a 40-year low in fiscal 2011—reaching 340,252, or about a fifth of what they were in 2000. That might sound like a success, until you consider that illegal immigration largely slowed because of the bad economy and that border agents have managed to basically do less with more.

For each border agent, there were 182 apprehensions in 2000. That average dropped to 16 by fiscal year 2011, according to U.S. Customs and Border Protection. Given the $3.5 billion budget for the CBP’s agent division, the cost per apprehension is $10,431, up from $630 in 2000. President Obama actually celebrated these numbers during his re-election campaign, but neglected to mention the price tag involved as he pledged to establish more pathways to residency.

“We've put more border patrol on than any time in history, and the flow of undocumented workers across the border is actually lower than it's been in 40 years,” he said during the Oct. 16 debate with Republican nominee Mitt Romney.

Republican politicians--most notably during the 2012 presidential primaries—claimed a massive fence should be expanded along Mexico, at a cost of as much as $20 billion. The U.S. has already committed to spending $700 million on 670 miles of fencing.

An official with the Customs and Border Protection told The Fiscal Times that the agency should not be judged by comparing its budget to apprehensions. The agency is still "working to implement performance measures that help further demonstrate the progress made in securing the border," the official said.

"Simply linking apprehension figures to CBP's overall budget is unhelpful as a means to determine the cost/benefit of border security," the official said. "Although apprehensions are one aspect of border enforcement, there are a number of critical outcomes that result from agents' efforts on the border, such as drug interdictions, arrests and successful prosecution of dangerous criminals, life-saving rescues, deterrence, increased situational awareness, and information sharing between state, local and international law enforcement partners."

But while lawmakers butt heads over how to trim the deficit, few dare to claim that additional savings could be achieved from scaling back the bureaucracy created to catch illegal immigrants. Budgets for the agencies involved—all of them under Homeland Security—have more than doubled over the past decade, despite some modest reductions in recent years for one of them, Immigration and Customs Enforcement.

NOT COMING BY CHOICE

By most analyses, it’s really the battered economy—rather than improved government vigilance—that explains what is driving the decline in illegal immigration. The numbers leaving Mexico (the largest source of illegal immigration to the United States) fell by more than two-thirds since the mid-2000s, according to Mexico’s 2010 census.

In short, the U.S. government has reached a point where it is either getting a much smaller return on its investment or is continuing to ratchet up spending to attack a problem that has greatly dissipated in recent years. This dilemma was highlighted in a new report by the Migration Policy Institute, a nonpartisan research group.

“In the face of new fiscal realities, immigration enforcement agencies and Congress will be forced to look at return on investment through a more strategic lens,” the report concluded. “A sharp focus on impact and deterrence – not simply growth in resources to combat mounting levels of illegal immigration – to determine funding and resource allocations is all but inevitable.”

Illegal immigrants have now become the country’s leading criminal targets, even though the report notes that a first-time illegal entry is a misdemeanor. Current spending for the core immigration enforcement agencies, including Customs and Border Protection, Immigration and Customs Enforcement, and the US Visitor and Immigrant Status Indicator Technology now dwarf all other criminal justice agencies—which in many cases have operations spanning the globe.

More than half of all prosecutions in federal court are for immigration-related crimes. Roughly twice as many people—429,247—are held in facilities run by Immigrations and Customs Enforcement than by the federal prison system, the study shows.

“What we need is to do smart sizing of our enforcement budget now,” Muzaffar Chishti, a co-author of the Migration Policy Institute study, told The Fiscal Times. “We may decide it doesn’t make sense for us to remove 400,000 people a year, half of whom are just garden variety immigration violators. . . . Our feeling is that additional funding will not produce more or better enforcement. We have in place enforcement machinery needed for the challenges of our country. What we need now is other elements of immigration reform which would improve enforcement itself.”

To be sure, the increased funding for Customs and Border Protection was designed to do more than stop illegal immigrants. The ramp-up in spending and formation of Homeland Security—the umbrella cabinet-level department for these agencies—was a response to the 9/11 terrorist attacks. The additional money on immigration enabled intelligence sharing with Mexican and Canadian counterparts. And it has also put a dent in the drug trade.

The number of drug and contraband seizures along the southwest border has surged by 83 percent to 18,898 over the past five fiscal years. But drug smuggling is “not used as a performance measure for overall border security” because other federal agencies such as the DEA have the primary responsibility, according to a Government Accountability Office audit issued last December.

The GAO found that the agency has not defined official performance metrics, so in the interim it has relied on the number of apprehensions.

“Border Patrol does not yet have performance goals and measures in place necessary to define border security and determine the resources necessary to achieve it,” the GAO said. “Border Patrol officials said that they had planned to establish such goals and measures by fiscal year 2012, but these efforts have been delayed, and are contingent on developing and implementing key elements of its strategic plan.”