WASHINGTON (AP) -- Neither Rick Perry nor Mitt Romney can claim conservative purity on illegal immigration -- and now both must deal with it.
Illegal immigration has emerged as a defining issue with remarkable staying power in a GOP presidential race that was expected to be primarily focused on the nation's struggling economy.
The heated clashes over illegal immigration between the two Republican presidential rivals in this week's debate made clear the issue isn't going away. It's a major fault line between them as they court a Republican primary electorate that generally takes a hard-line view against people who are in the country illegally.
At every turn, Perry, the Texas governor, has been forced to defend his signing of a law that allowed some illegal immigrants to get in-state college tuition. And now Romney is having to answer for the fact that some groundskeepers who had worked on his lawn were in the country illegally.
"Mitt, you lose all of your standing from my perspective because you hired illegals in your home, and you knew about it for a year," Perry told the former Massachusetts governor at Tuesday's debate in Las Vegas. "And the idea that you stand here before us and talk about that you're strong on immigration is, on its face, the height of hypocrisy."
Romney countered, "Rick, I don't think that I've ever hired an illegal in my life" and challenged his rival to show him the facts.
It was a preview of what Republicans can expect to hear in the coming weeks as the Jan. 3 leadoff Iowa caucuses inch closer, with Romney and Perry emerging as the two candidates with the best chances of winning the nomination. They're arguably the only Republicans with the money and organization necessary to go the distance.
For months now, immigration concerns have followed presidential contenders to town hall meetings from Nevada to Iowa to New Hampshire. And in some ways, immigration has shaped the increasingly bitter Republican nomination fight more than any other issue, particularly in a crowded field where the conservative candidates have more in common than not. And while conservative voters may be driving immigration chatter on the campaign trail, the candidates are stoking voter passions when given the opportunity.
"I'm not surprised that immigration is playing as big a role as it is," said Kevin Smith, a likely New Hampshire Republican gubernatorial candidate who has watched the candidates face repeated questions about the topic on the campaign trail. "This issue plays very well with Republican primary voters."
And it's clear they're listening.
Perry's sudden drop in the polls was largely attributed to weak debate performances involving his support for the Texas law. He suggested that Republicans who oppose the policy were heartless. And Romney fueled the tuition criticism every chance he got.
But Perry tried to neutralize the attacks this week. The outspoken Texan raised new questions at the debate about Romney's use of a landscaping company that employed illegal immigrants at his suburban Boston home several years ago.
For a moment, it looked as though Perry and Romney may come to blows as they debated the issue, with Romney at one point putting his hand on Perry's shoulder as the conversation began to heat up.
"The American people want the truth," Perry demanded. "They want to hear you say that you knew you had illegals working at your ..."
Romney cut in: "Would you please wait? Are you just going to keep talking, or are you going to let me finish with my -- what I have to say?"
For Romney, it was a frustrating return to an issue that played out in his 2008 presidential campaign.
At that time, and again Tuesday night, he said he had little control over whether a landscaping company he legally hired had illegal immigrants on the payroll. But the exchange provided one of the few moments in this presidential campaign in which the usually poised Romney showed flashes of anger.
That anger was apparent in campaign rhetoric from both sides the day after the debate.
"Gov. Perry is desperate to deflect from his liberal immigration record," Romney spokesman Ryan Williams said, calling Perry's launching of "a personal and untruthful attack" on Romney "unpresidential."
But don't expect Perry to back down from an issue that may have fueled his strongest debate performance.
Perry spokesman Ray Sullivan said, "Mr. Romney has been demagoguing and distorting these immigration and border control issues for months now." Sullivan argued that Romney was "exposed as someone who had illegal immigrants working in his lawn and cleaning his tennis court."
Sullivan would not say whether Perry might exploit the issue in television advertising, but he hinted that Romney has only seen the beginning of the new criticism.
There is danger is pushing too hard on immigration.
Polling suggests the issue may help the candidates score political points with Republican primary voters but could alienate the ballooning Hispanic population or hurt the candidates among independents in a general election matchup against President Barack Obama.
Obama campaign manager Jim Messina seized on the issue Wednesday.
"Romney's been taking hard-right positions on the campaign trail on immigration. He didn't object to having undocumented workers working for him because it's illegal; he objected because he thought it would hurt his political career," Messina said.