But the Obama administration contends that it has invested more heavily in enforcement efforts than ever before. Several high-profile studies have found that the federal response has helped reduce the flow of illegal immigrants, bringing net migration between the United States and Mexico to a virtual standstill.
Last year, the government spent $18 billion on immigration control, 24 percent more than all other federal law enforcement agencies combined, according to a study released this month by the nonpartisan Migration Policy Institute. The Obama administration deported nearly 410,000 people in 2012 — a record, and 25 percent more than in 2007.
At the same time, the number of people apprehended at the Mexican border trying to enter the United States dropped to 340,000, a 40-year low, in 2011. Immigration advocates say the decline shows that the heavy investment in border agents and surveillance technology has effectively deterred foreign nationals from attempting to cross.
Obama administration officials also say the government has largely met, and in some cases surpassed, enforcement benchmarks set in 2007, when a comprehensive immigration reform bill failed in the Senate in part because of concerns about border control.
“I certainly feel very comfortable saying that never before has the border been as protected as it is now,” said Nestor Rodriguez, a sociology professor at the University of Texas who has studied immigration from Mexico and Central America. “The large undocumented population is partly a result of that success: People are afraid to go back home because it’s hard to get back in.”
That progress, advocates say, largely renders moot the demand from leading Republicans, including Sen. Marco Rubio (Fla.), that a path to citizenship for illegal immigrants be contingent on stricter border-control measures that remain largely undefined.
“Incredible resources have been spent on the interior and border enforcement, and we need to make sure the road to citizenship is not subject to that,” said Marielena Hincapie, executive director of the National Immigration Law Center. The GOP position “raises the question of whether the border can ever be completely secured and is that road to citizenship even achievable or not?”
The issue is quickly emerging as a key obstacle in the latest round of immigration reform negotiations. Talk show host Rush Limbaugh pressed Rubio on Tuesday to vow he would not support a path to citizenship without tying it to stricter border control.
“If there is not language in this bill that guarantees that nothing else will happen unless these enforcement mechanisms are in place, I won’t support it,” Rubio responded.
Obama has also emphasized that he supports increased enforcement at the border as a key element of any immigration plan. But he did not endorse a proposal this week from Rubio and seven other senators that would establish a border commission to monitor security and make recommendations that would be used as a “trigger” to allow undocumented migrants to pursue citizenship.
Administration officials and advocates fear such a mechanism could create long delays and create a class of legal residents without full benefits.
With border apprehensions plummeting in recent years, most experts agree that the number of migrants attempting to enter the United States illegally has probably dropped sharply. They attribute the trend to several factors, including reduced labor demand in the United States as the result of a sluggish economy.
Still, the experts agree that federal enforcement is also a likely reason for the reduced flow. Increased federal funding has paid for more than 21,000 federal agents at the border with Mexico, 651 miles of fencing, 300 camera towers and nine surveillance drones to monitor remote areas.
Last April, the Pew Hispanic Center found that the net migration between the United States and Mexico had fallen to zero, reversing four decades of “the largest wave of immigration in history from a single country to the United States.”
Marc Rosenblum, an immigration policy specialist for the Congressional Research Service, wrote in a report last year that Congress “may consider the possibility that certain additional investments at the border may be met with diminishing returns.”
Republicans argue that as the U.S. economy improves, the flow of undocumented workers is likely to pick up again. And they cite a report last month from the Government Accountability Office that determined that the U.S. Border Patrol was intercepting just 61 percent of migrants who attempted to cross illegally into the country from Mexico.
That study found that the agency was unable to apprehend nearly 209,000 migrants at the border, of which about 86,000 successfully escaped into the United States. Both numbers, however, were down significantly from 2006.
“There has been some progress,” said House Homeland Security Committee Chairman Michael McCaul (R-Tex.). “But the bottom line is that we are far from having operational control of our borders.”
Rubio and other GOP leaders also include improved workplace verification of immigration status as part of the broad conversation over enforcement. Democrats, including Obama, agree that new safeguards must be established to help employers identify undocumented workers.
Some conservatives view worker identification as a more vital issue. Mark Krikorian, executive director of the Center for Immigration Studies, which promotes stricter immigration control, said the border commission proposed by the Senate working group is “a gimmick” that has little value but is designed to appeal to conservatives who would otherwise reject comprehensive reform efforts.
“It’s easier to talk about fences and border-control agents than it is to deal with the more difficult issues of work-site enforcement,” Krikorian said.
The National Association of Retired Border Patrol Officials has opposed allowing illegal immigrants to become legal residents, saying it rewards lawbreakers. But many retired agents agree that the number of illegal migrants has fallen dramatically.
“We have never seen the level of control we have now,” said David B. Ham, a retired Border Patrol officer and president of the National Border Patrol Museum in El Paso. “The numbers are way down — there’s no doubt.”
Pamela Constable contributed to this report.