At opposite sides of New Hampshire, John McCain faced two corporate audiences in two college towns earlier this month. Only one topic came up in both places when he starting taking questions: illegal immigration.

The Republican presidential hopeful gets so many questions -- sometimes hostile -- about immigration at his town hall meetings that he quips, "This meeting is adjourned," before explaining his position at length.

In a recent Associated Press-Pew Research Center poll, 17 percent of likely Republican voters in the New Hampshire's first-in-the-nation presidential primary named illegal immigration as the one issue they want to hear candidates talk about, making it second only to Iraq. In Iowa, where caucuses kick off the presidential nominating season, immigration was the leading issue for 18 percent of Republicans, ahead of Iraq.

New Hampshire is a state of 1.3 million people, with a small immigrant population and even smaller illegal one. There were 14,000 more foreign-born residents in the state last year than in 2000, according to the U.S. Census Bureau. A report last year by the Pew Hispanic Center estimated the state is home to somewhere between 10,000 and 30,000 illegal immigrants.

Andrew Smith, director of the University of New Hampshire Survey Center, said he has believed for a year or so that illegal immigration would be important in the GOP primary because it strikes so many chords. There's the economic argument: Illegal immigrants are taking jobs from Americans. There's the legal one: They're breaking the law. There's the cultural argument: They're not assimilating into American culture. And then there's what Smith calls the "racial overlay."

"You've got all these different facets of this issue, which is just primed and ready to go off," said Smith, whose most recent poll also had immigration as the number two issue for New Hampshire Republicans.

It doesn't matter that New Hampshire has little direct experience.

"It's the kind of issue that you don't have to be impacted by it personally to be concerned about," Smith said.

"It's costing those of us who work and pay taxes millions and millions of dollars to support these people who shouldn't be here in the first place," said JoAnn Sherman, 54, of New Boston, N.H. "They're getting free health care, they're getting schooling for their children. Yes, they're working, but they're not paying taxes. They're here, and being a drain more than they're producing."

"And it goes along with the terror issue because it's telling us we don't know who's in this country," she said.

White House Challenges Assumptions

The White House, which has long sought what it calls a comprehensive approach to updating the nation's immigration laws, released a report in August that said immigrant workers find employment that tends to complement -- not replace -- the jobs held by workers born in the United States.

On average, native-born U.S. workers' wages have been boosted as immigrant workers have helped to expand the nation's overall economic pie and thus its wealth by billions of dollars a year, the report said.

It also found that immigrants make up 15 percent of all workers, and larger shares of occupations such as construction, food services and health care. About 40 percent of Ph.D. scientists working in the United States were born abroad.

The White House also said immigrants and their children assimilate into U.S. culture. For example, although 72 percent of first-generation Latino immigrants use Spanish as their predominant language, only 7 percent of the second generation are Spanish-dominant.

The paper acknowledges the challenges of U.S.-born workers with little education, but adds that "it is safe to conclude that immigration is not a central cause of those difficulties, nor is reducing immigration a well-targeted way to help these low-wage natives."

Rivals Mine Issue For Votes

GOP state chairmen in both New Hampshire and Iowa say concerns about national security have made illegal immigration a top issue in their states.

Former Massachusetts Gov. Mitt Romney has proposed bolstering border patrols, creating employment eligibility cards and penalizing employers who hire illegal aliens who lack the cards. He also has criticized rival Rudy Giuliani for discouraging the prosecution of illegal immigrants while he was mayor of New York - an accusation Giuliani deflected in a recent debate by pointing out that Romney had illegal immigrants work on his lawn.

Former Arkansas Gov. Mike Huckabee recently released an immigration plan that takes a tough stance similar to those taken by Romney and other GOP rivals. But Huckabee has been more forgiving in the past of some here illegally: As Arkansas governor, he attempted to make children of illegal immigrants eligible for scholarships and in-state college tuition.

Huckabee defends those moves.

"In all due respect, we are a better country than to punish children for what their parents did," he said last month.

McCain, meanwhile, has regained some of the support he lost last spring when he was pushing a comprehensive immigration bill that ultimately failed in Congress. He still supports a path to citizenship for illegal immigrants, but has emphasized recently that securing the borders must come first.

Slideshow | Interactive | Newsletter

In Durham, N.H., McCain told the skeptical employees at Goss International that under his bill, illegal immigrants seeking to become citizens would have had to pay fines and get in line behind those here legally. But he also offered a broader perspective.

"They are God's children. They are human beings. Many of them come just because they need a job. And I think many of them, as you know, are badly exploited and mistreated by these coyotes and others," he said. "So I think we ought to be sure we look at the humanitarian side of this issue to try to make sure that all human beings are endowed by their creator with certain inalienable rights, whether they are citizens of this country or not."