Key question in immigration debate: Are the borders secure enough?

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.