Mitt Romney ended his struggling US presidential bid on Thursday, clearing the way for John McCain to become the all-but-certain Republican nominee and begin mending fences with disgruntled party conservatives.
In an appearance before a conference of conservative activists, Romney said he was ending his bitter nominating duel with McCain to allow Republicans to focus on a November election showdown with the eventual Democratic nominee, either Sen Hillary Clinton or Sen Barack Obama.
"I feel I have to now stand aside, for our party and for our country," the former Massachusetts governor told the shocked crowd, some of whom gasped and shouted "no, no" in response.
McCain, who had built an almost insurmountable lead in delegates to the party's nominating convention, pleaded for party unity during an appearance at the same conference a few hours later.
"I know I have a responsibility, if I am, as I hope to be, the Republican nominee for president, to unite the party and prepare for the great contest in November," the Arizona senator told the activists gathered in a Washington hotel.
"And I am acutely aware that I cannot succeed in that endeavor, nor can our party prevail over the challenge we will face from either Senator Clinton or Senator Obama, without the support of dedicated conservatives," he said.
Romney pulled out after losing 14 of 21 states on Tuesday, the biggest day of US presidential voting ahead of November's election, while McCain romped to coast-to-coast wins and cemented his position as front-runner.
Former Arkansas Gov Mike Huckabee, who won five states on Tuesday, remains in the race but will have an almost impossible task overcoming McCain, who has rolled up more than 700 of the 1,081 delegates needed to win the nomination.
McCain, the 71-year-old former Vietnam prisoner of war, has become a target of critics on the right for his moderate views on illegal immigration, his votes against President Bush's tax cuts in 2001 and 2003 and his labeling in 2000 of some religious conservative leaders as "agents of intolerance."
McCain's name was booed by some members of the audience when Romney mentioned him, but he drew mostly cheers when he appeared before the crowd, many of them McCain supporters brought in by the campaign.
Draws some boos
He drew boos, however, when he brought up his support during last year's Senate debate for a path to citizenship for illegal immigrants. McCain has since said border security must come first.
"It is my sincere hope that even if you believe I have occasionally erred in my reasoning as a fellow conservative, you will still allow that I have, in many ways important to all of us, maintained the record of a conservative," McCain told the conference.
"I am proud to be a conservative," he said.
McCain said he had spoken to Romney, congratulated the governor and added they had agreed to sit down together at a later date.
Some attendees said they were disappointed Romney was leaving, calling him the only conservative candidate in the race.
"This leaves me very concerned about the future of the Republican Party," said Nathan Shapiro, 22, a college student in New York. "I don't think McCain will carry on the traditions of the Republican Party, he's not a real conservative."
Romney said he was pulling out of the race in order to let Republicans prepare for a general election battle against the two remaining Democrats, both whom have campaigned to withdraw U.S. troops from Iraq.
"In this time of war, I simply cannot let my campaign be a part of aiding a surrender to terror," he said.
Romney, 61, had vowed to fight on after Super Tuesday, but the abrupt reversal followed a meeting with advisers on Wednesday. Romney, a former venture capitalist, has spent more than $35 million out of his own pocket to fund his campaign.
"This is not an easy decision for me. I hate to lose," an emotional-looking Romney said.
Many Republicans are eager for an end to the nominating contest between McCain, Romney and Huckabee in order to begin what is expected to be a difficult fight against either Clinton or Obama.
Romney's decision will raise pressure on Huckabee to do the same, although he has said he will continue his run fueled by evangelical Christians.
Romney said he did not want to extend a fight that could possibly last until Republicans hold their nominating convention in late summer.
"If I fight on in my campaign, all the way to the convention, I would forestall the launch of a national campaign and make it more likely that Sens. Clinton or Obama would win," Romney said.
Romney did not endorse McCain in his speech. The two have engaged in a bitter cross-fire in recent weeks over who is the real conservative.