Republican presidential candidate Mitt Romney urged conservatives to overcome their doubts and get behind him to take on President Barack Obama in this November's election.
Facing a surprise challenge from Rick Santorum, Romney laid out his credentials at a prominent meeting of conservatives in Washington where he was well received.
"I'm here to ask you to stand with me shoulder-to-shoulder as we fight for America," Romney said in a speech to the Conservative Political Action Conference.
Speaking to the same forum, Santorum tried to sow doubts about the electability of Romney as the chief rivals for the Republican presidential nomination courted conservatives with pledges of fidelity to their causes.
Describing himself as "severely conservative", Romney said he would make no apologies for his vast wealth earned as a private equity executive at Bain Capital.
"I spent 25 years balancing budgets, eliminating waste, and keeping as far away from government as was humanly possible. I did things conservatism is designed for. I started new businesses and turned around broken ones. And I am not ashamed to say that I was successful in doing it," Romney said to loud applause.
Romney mentioned his rivals only indirectly. He said his opponents are "creatures of Washington" and that he is the only candidate left in the race who has never worked a day in the U.S. capital.
Romney got a strong reception, several standing ovations and heavy applause - a better response than received by Santorum when he spoke earlier in the day. In addition, Romney got key support from some of the speakers.
Conservative firebrand Ann Coulter called Romney "the most conservative" candidate of the four remaining and Al Cardenas, president of the American Conservative Union, said Romney meets the conservative test.
Romney's losses to Santorum in nominating contests in Missouri, Michigan and Colorado this week raised doubts about his front-runner status and put pressure on him to convince conservatives to support him as the best candidate with a chance to defeat Obama.
Santorum's wins in the three states on Tuesday have given him a burst of momentum and a reason to promote himself as Romney's main conservative alternative in the weeks leading up to March 6, the Super Tuesday when 10 states vote.
He presented himself as the true conservative in the 2012 race and said Romney's more moderate record does not draw enough of a contrast with Obama.
Santorum criticized the view held by many Republicans that while Romney is not the most conservative hopeful, he would be a strong candidate in the November 6 election against Obama because he would appeal to swing voters.
"Why would an undecided voter vote for a candidate that the party's not excited about?" Santorum said.
He took aim at Romney's healthcare plan developed when he was Massachusetts governor, calling it "the stepchild of Obamacare," the White House overhaul that conservatives want to repeal. Romney says he would repeal it if elected.
And Foster Friess, a Santorum backer who introduced him on stage, told a joke aimed at bolstering a stereotype about Romney, that he has flip-flopped on many positions.
"A liberal, a moderate and a conservative walked into a bar. And the bartender said, 'Hi Mitt,'" he said.
Santorum, accompanied by his family on stage, spoke passionately for conservative values. Vastly outspent by Romney, Santorum made a plug for fund-raising and said the election will not be decided on money but on ideas.
"Conservatives need conservatives now to rally for a conservative, to go into November to excite the conservative base, to pull with that excitement moderate voters and to defeat Barack Obama in the fall."
Santorum will have to deal with the views of conservatives like Molly Edwards of Washington, North Carolina, who came away from Romney's speech believing he is a true conservative and able to beat Obama.
"I think he has made it clear that he is a conservative and he is the only candidate who can beat Obama because he also will appeal to independents and moderates," she said.