WASHINGTON Listening to the Republican White House aspirants talk about illegal immigration, voters might not know that attempted border crossings are at a 40-year low.

With slight variations, the top GOP candidates back mass deportations of illegal immigrants, tough state enforcement laws and extending the 675-mile fence along the U.S.-Mexico border. They also oppose giving most illegal immigrants a path to legal residency.

"Border crossings are at a historic low, deportations are at a historic high, yet every Republican presidential candidate says the first thing we have to do is secure the border," said Frank Sharry, executive director of America's Voice, a Washington group that wants immigration enforcement to focus on serious criminals and national security threats.

The issue is likely to heat up as the candidates campaign for South Carolina's Republican primary Jan. 21.

Illegal immigration has long been a hot-button topic in South Carolina, where U.S. Sen. Jim DeMint was lionized by Republican activists for his leading role in killing 2007 reform legislation he branded as amnesty.

Conservative radio commentator Rush Limbaugh mocked U.S. Sen. Lindsey Graham, R-S.C., as "Senator Grahamnesty" for his efforts to pass the measure. Graham has since adopted harder positions on immigration.

Leaders warn of alienation

Influential Republicans have warned about reversing the inroads that President Ronald Reagan, President George W. Bush and 2008 GOP nominee John McCain made among Hispanics, the country's fastest-growing demographic group with 21.7 million eligible voters - almost three times the number in 1988.

"The Republican Party has to discuss (immigration) in as humane a way as possible," McCain told CNN last month. "We have to have empathy; we have to have concern, and we have to have a plan."

Former Bush adviser Karl Rove and former House Republican leader Dick Armey also have warned against alienating Hispanics.

Former Sen. Rick Santorum's calls for mass deportations and opposition to any leniency helped him in Iowa, where he came within eight votes of defeating Romney in last week's GOP caucuses.

Romney and other rivals pilloried former House Speaker Newt Gingrich for saying in a November debate that undocumented workers who've been in the country for decades should be given a chance to gain legal status.

Some see a missed opportunity

Hispanic lawmakers and advocates find irony in the claims by DeMint, Romney, Santorum and other Republicans that President Barack Obama has been soft on illegal immigration.

The federal government deported a record 395,000 foreigners in 2009 and 387,000 in 2010, compared with 189,000 in 2001 and 165,000 in 2002 - George W. Bush's first two years in office. The number of illegal immigrants in the U.S. has dropped to 11.2 million from its peak of 12 million in 2007.

Some analysts say the GOP candidates' attacks on illegal immigration could sabotage a chance to cut into Obama's political base.

"By being so anti-immigrant, the Republicans are missing a huge opportunity," said Clarissa Martinez, who will direct get-out-the-vote efforts for the National Council of La Raza, an advocacy group based in Washington. "They are pushing Latinos towards the Democrats."