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“What’s remarkable is they followed the playbook on abortion and gay marriage, but not immigration. I am, just from a political point of view, flabbergasted that he has run so far to the right on this issue, and what that will do to his electability in the general election,” he said. “And so what? So he can be more conservative than Rick Perry and Newt Gingrich? As if it’s the defining issue of the conservative base? It’s not.”

All of that makes Mr. Romney the most vociferous opponent of illegal immigration in the field.

The contrast between the former governor and Mr. Obama was underscored this week when Mr. Romney trumpeted the endorsement of Mr. Kobach, while at the White House Mr. Obama gave a promotion to Cecilia Munoz, a chief backer of the legalization bill Mr. Bush and Sen. Edward M. Kennedy, Massachusetts Democrat, tried to push through the Senate in 2007. Ms. Munoz was at the National Council of La Raza at the time, left that group to join the White House in 2009, and on Monday was promoted to run the White House’s Domestic Policy Council.

“It just goes to show that Obama is trying to close down his vulnerability with Hispanic voters, and Romney is opening up his,” Mr. Sharry said.

After Mr. Romney’s promise to veto the Dream Act, students have begun to follow him and challenge his position.

In an interview with The Times this weekend, Mr. Romney didn’t back down, saying he doesn’t see much room for exceptions to his policy that illegal immigrants should go home.

“I will put out a series of immigration proposals before November of 2012, and I will look at adjustments to the law that I think maybe necessary, but my principle is straightforward and that is that those who’ve come here illegally really should not be given a preferential path to permanent residency or citizenship,” he said.

Hispanic voters are considered a critical swing group in the upcoming election, and Mr. Romney has said he needs to do well in attracting them.

The Republican National Committee also is committed to the effort, and on Wednesday it announced its Hispanic voter-outreach program, calling Hispanics “essential” to the GOP’s 2012 election.

One early test for the GOP and Hispanic voters will come Jan. 31 when Florida holds its primary. Mr. Romney on Wednesday announced a Spanish-language ad he is running in that state, featuring his son Craig and three Cuban-American Republicans, two of whom are in Congress and the other of whom is a former member.

Seth McLaughlin contributed to this article from New Hampshire.