Washington (CNN) -- Republican presidential front-runner Mitt Romney told a gathering of conservative leaders and activists Friday that it won't be enough to point out how Democrats failed, but that Republicans also need to lead if they want to take back the White House.
Romney's address to the Conservative Political Action Conference was seen as an opportunity to assure conservatives he shares their values. The former Massachusetts governor hasn't been able to capture the party's base, as evidenced by rival Rick Santorum's stunning sweep of three caucuses and primaries Tuesday.
Santorum's wins have slowed Romney's run to the nomination, which had regained momentum after back-to-back wins in Florida and Nevada.
"I was a severely conservative Republican governor," Romney told the audience of his time in office, pointing out his support of traditional marriage and abstinence education.
Romney has been basically running against President Barack Obama since he entered the race, wavering from that path only to attack his rivals when they threatened his front-runner status. Over the last few days, he has focused most of his attention on Santorum.
Santorum spoke to the group earlier Friday, directing most of his remarks toward Obama, although he used one of them to take a swipe at Romney, saying the president's health care law passed over conservative opposition was the "stepchild of Romneycare," referring to health care legislation passed under Romney's watch in Massachusetts.
Former House Speaker Newt Gingrich used his CPAC speech to portray himself as the heir to Barry Goldwater's and Ronald Reagan's conservative movement, slamming a GOP establishment that lacks the "toughness," "commitment," and "philosophy" necessary to build a political majority.
Blasting establishment "timidity that comes from managing the (country's) decay," Gingrich promised to immediately repeal Obama's health care reform and financial regulatory reform while also replacing the Environmental Protection Agency and eliminating the Energy Department, among other things.
"This is the year to reset the country in a decisive, bold way," Gingrich declared. "This is going to be a big choice, big decision election."
Rep. Ron Paul of Texas, the fourth major Republican candidate, was invited but opted to stay on the campaign trail, according to the American Conservative Union, which hosts CPAC.
Romney traveled to Maine later on Friday for a town hall on the eve of the announcement of the winner of that state's GOP caucuses.
At that meeting, he again hit on his conservative credentials, telling the crowd it was time to "return to conservative principles," and focus on the "principles and values in our founding documents."
Santorum, in his address, spoke about the controversy over the Obama administration's proposal to require that insurance provided for female employees at religiously affiliated institutions cover birth control, saying there is little need for insurance to cover what he said is relatively inexpensive birth control medication.
"It is not about contraception," he said. "It is about economic liberty. It is about freedom of speech. It is about freedom of religion. It is about government control of your lives and it has got to stop."
Santorum's remarks came about the same time the administration was announcing a compromise proposal exempting more religious institutions from having to provide the coverage, but requiring their insurers to offer contraception coverage at no charge.
Gingrich warned that Obama is planning to "wage war on the Catholic Church the morning after he's reelected."
While Romney used most of his time on the CPAC stage to try to present his conservative bona fides, he also tried to make distinctions between himself and Obama -- both Gingrich and Santorum have tried to topple him from the head of the pack by painting his policies as synonymous with Obama's.
Romney also got in one swipe at his top two challengers while portraying himself as a Washington outsider compared to Gingrich, the former House speaker who resigned his post, and Santorum, whom Romney has hammered over his record on earmarks during his time in Washington.
"I am the only candidate in this race, Republican or Democrat, who has never worked a day in Washington," he said. "I don't have old scores to settle or decades of cloakroom deals to defend."
Romney started his day with remarks to the Northern Virginia Technology Council, delivering a speech focusing on "dramatic, bold, creative change," including fewer regulations and a tax structure that he said would encourage risk-taking to position the United States as the most innovative nation in the world.
"If America is to remain the strongest nation on earth, then we must be the most innovative nation on Earth," Romney said before laying out what he said are autocratic challenges to U.S. preeminence in the world.
Romney ends the week in a more tenuous position than he began it after Santorum swept the three Republican contests on Tuesday.
Colorado was the most competitive state on Tuesday, with Santorum winning 40% of the vote to 35% for Romney, 13% for Gingrich and 12% for Texas Rep. Ron Paul
In Minnesota, Santorum got 45% of the vote to 27% for Paul, 17% for Romney and 11% for Gingrich, according to the secretary of state.
In Missouri, Santorum had 55% to Romney's 25% and 12% for Paul, according to unofficial results. Gingrich didn't make the ballot there.
Santorum's victories in two states Romney won in his unsuccessful 2008 presidential bid -- Colorado and Minnesota -- signaled both his growing support and Romney's inability to build on the momentum from victories in the two previous contests in Florida and Nevada.
They also helped Santorum in the fund-raising department. The super PAC that supports Santorum, the Red, White and Blue Fund, has seen increases in contributions and pledges since Tuesday night.
"We've been working at a speed faster than any other day the super PAC has seen in this election season," Stuart Roy, a spokesman for the PAC, told CNN.
Romney's campaign promised to challenge Santorum more directly after Tuesday's results, and followed through Thursday by attacking the former Pennsylvania senator as a Washington insider. Romney accused Santorum and Gingrich of behaving more like Democrats during their time in Congress.
After Saturday's announcement of the winner in Maine, the GOP contest to take on Obama moves to Arizona and Michigan on February 28.
CNN's Kevin Bohn, John Helton and Michael Pearson contributed to this report.