WASHINGTON -- On the day he became the presumptive Republican nominee, John McCain was greeted with a mix of cheers and lusty boos as he tried to persuade wary conservatives that he shares their values.
McCain's much-anticipated appearance at a conservative conference yesterday came only hours after former Massachusetts Gov. Mitt Romney stunned the same audience by announcing that he was quitting the presidential race.
Former Arkansas Gov. Mike Huckabee is now the Arizona senator's only serious challenger. But party strategists said Huckabee has no realistic chance of overtaking the front-runner in the remaining primaries.
"Senator McCain has a prohibitive lead," said Whit Ayres, a Republican pollster who is not aligned with any campaign.
Huckabee said he had no plans to get out and appealed to Romney supporters to back him as "a true authentic, consistent, conservative."
McCain's immediate task, as he tries to solidify his grip on the nomination, will be to unite conservatives, whose support he called "indispensable to the success of our party." As the decidedly mixed reaction he got at the Conservative Political Action Conference suggested, that won't be easily accomplished.
"I have made many mistakes. You can attest to that, but need not, need not," he said to laughter and applause.
Before, during and after his remarks, there were scattered boos by a significant minority of the audience, made up largely of those under 30.
The hostility was particularly noisy when he turned to his stance on immigration, "a position which obviously still provokes the outspoken opposition of many conservatives," McCain said, smiling until the audience reaction subsided.
His authorship of an immigration reform measure, with liberal Democratic Sen. Edward M. Kennedy, nearly sank his candidacy. Critics said the path to citizenship under the plan, which failed to gain Senate approval, amounted to amnesty for an estimated 12 million illegal immigrants.
"I stood my ground, aware that my position would imperil my campaign," said McCain, who now refuses to say that he would sign the measure, if he became president.
McCain, a pragmatist whose efforts at bipartisanship in Congress have enraged many conservatives, called himself a mainstream conservative who remains proud of his association with Ronald Reagan. He said he was "acutely aware" that he wouldn't be able to win in November without conservative support.
To skeptics who doubt the sincerity of his conservative rhetoric, McCain said that he had backed up his fiscal and social conservative values with a 24-year anti-abortion voting record in Congress, repeated opposition to gun control and support for "judges who enforce, and not make, our laws."
He listed a string of campaign positions he had taken, at what he said was considerable political risk, that illustrated his "genuine convictions." Among them: opposition to agriculture subsidies while campaigning in Iowa and to a national catastrophic insurance fund measure in Florida.
There was enthusiastic applause when McCain called for making Bush's 2001 and 2003 tax cuts permanent, without alluding to his Senate votes against them. He also skirted other issues, such as campaign finance reform and global warming, on which his views have alienated conservatives.
In an appeal that audience members later said had drawn a strong emotional response, McCain referred to his experiences as a Vietnam prisoner of war in emphasizing his service to country and love of freedom.
"I know that to be denied liberty is an offense to nature and nature's creator," he said. "I will never waver in that conviction, I promise you."
A cadre of popular conservative talk show hosts and former Republican officeholders has been waging a Stop McCain campaign, and many grass-roots conservatives remain deeply distrustful of the likely nominee.
McCain hopes to bring them around by arguing the dangers of electing Hillary Clinton or Barack Obama. He devoted a portion of his speech to issues, such as the war in Iraq, taxes and the appointment of federal judges, that he said would define the fall campaign against one of the Democratic senators.
Some prominent conservatives, from James Dobson of Focus on the Family to talk show host Ann Coulter, have said they won't vote for McCain. Former Republican leader Tom DeLay has said that McCain's nomination would destroy the party.
Laura Ingraham, another conservative talker, took a sneering shot at McCain while introducing Romney yesterday.
"I don't think it's enough to say that you were a foot soldier in the Reagan revolution," she said. "I think the question is what have you been doing for conservatism lately?"
Jason Mattera, 24, of Brooklyn, N.Y., who works for a conservative organization, was among those booing McCain.
"The issues he's bad on, he's really bad on," Mattera said, including campaign reform. "When you work with Ted Kennedy, who is one of the most liberal lions of the U.S. Senate, you are not advancing your ideals."
Daniel Lipian, a student at Bowling Green State University and head of college Republicans in Ohio, said he would sit out the November election because of McCain's "liberal voting record" and views on global warming, immigration and restrictions on money in politics.
Cleta Mitchell, a conservative legal activist, said the "fissures are deep" on the Republican right.
"He's got nine months to give birth to a conservative support group," she said, but that no one should expect McCain to become a different person.
"He's not going to change. He's 70,000 years old," said Mitchell, adding that it was an open question whether she would vote for him or stay home.
Donald Devine, a conservative strategist from Maryland, said he doubted that McCain's speech changed any opinions. Most conservatives will vote for McCain anyway, he said, but otherwise won't do much to assist him.
"Really, the only thing that he could do that would really help at this point is to pick a vice president that conservatives could really get excited about," Devine said.