COLUMBIA, S.C. - Pledging fidelity to the Constitution and vowing to carry the tea party's priorities to the White House, the Republicans chasing the GOP's presidential nomination pitched themselves Monday to their party's libertarian activists as the strongest candidates to roll back four years of President Barack Obama's tenure.

Former Massachusetts Gov. Mitt Romney said the Obama administration flouted the Constitution to push a political agenda. Rep. Michele Bachmann of Minnesota stridently called Obama's policies "unconstitutional" at the same tea party-backed forum on Labor Day. And Texas Gov. Rick Perry, the third member of his party's top tier, told a separate town hall-style audience earlier in the day that he has a better record on jobs than the president.

With Labor Day marking the unofficial start to the 2012 campaign, the contenders were painting themselves to the tea party during an afternoon forum with Sen. Jim DeMint in his home state - site of the first nominating contest in the South. The event was designed to probe the candidates on their views of spending, taxes and the Constitution - bedrock principles for the tea party activists whose rising clout is likely to shape the nominating process.

"I don't think I've ever seen an administration who has gone further afield from the Constitution ... than the Obama administration, not just with regulation, but with energy policy, with financial regulatory policy and, with the worst example, Obamacare," Romney said, outlining conservatives' broad indictment of Obama's tenure.

It also was a prime opportunity for the candidates to level pointed - though, in many cases, familiar - criticism of Obama.

"The track record we have creating jobs, I'd put up against anyone running for president of the United States, particularly the current resident of the White House," said Perry, whose late entry into the race threatens Romney's one-time aura of inevitability with support from tea partyers.

And Bachmann sought to sustain her status as a movement darling and suitable alternative to Romney. Although she never engaged him directly, her remarks seemed centered on Romney.

Bachmann warned that Obama and Democrats' health care legislation was taking away freedoms and giving Washington abject power.

"They will become a dictator over our lives," she said of federal requirements included in the overhaul that requires Americans to have health insurance. Massachusetts requires a similar mandate.

"This is the foundation for socialized medicine. Make no mistake about it. It will change the face of this nation forever," she warned.

After keeping the tea party at arm's length most of this campaign, Romney appeared at two tea party-related events this holiday weekend, first in New Hampshire on Sunday and then Monday here. He slightly tweaked his pitch and acknowledged critics of Massachusetts' health plan.

"Our bill dealt with 8 percent of our population, the people who weren't insured," Romney said.

"He dealt with 100 percent of American people. He said, 'I'm going to change health care for all of you.' It's simply unconstitutional. It's bad law. It's bad medicine. ... It has got to be stopped and I know it better than most."

Aware of the tea party's potential to pick the nominee, all candidates have tailored their pitches to appeal to the libertarian and grassroots activists.

Bachmann, a former federal tax lawyer, called the Constitution "that sacred document" and challenged Obama's understanding of his powers under it. She cited Obama's advisers, whom she called "czars," the Justice Department's decision not to appeal a court's overturning of a federal marriage law, and his immigration policies.

"These are areas where we see unconstitutionality," she said of Obama, a Harvard Law School graduate and former constitutional law lecturer at the University of Chicago.

Former House Speaker Newt Gingrich played up the founding fathers' writings on liberties during his appearance: "These rights are inalienable. That means no politician, no bureaucrat, no judge can take that away from you."

Rep. Ron Paul of Texas, a favorite of the GOP's libertarian wing, decried government largesse: "People were supposed to carry guns, not bureaucrats." He also warned against a Washington that gives the Federal Reserve too much power, a favorite rallying cry for his steadfast supporters.

And pizza magnate Herman Cain of Georgia, who does well during these forums with amusing quips but hasn't built a serious campaign organization, again was critical of Washington.

"The idea in Washington, D.C. ... is if you reduce the growth, that's a cut," he said. "That's not a cut. That's deceiving the American people."

Ahead of the forum, Perry spoke at a town hall-style meeting before heading home to Texas in a last-minute schedule change to monitor raging wildfires. He phoned DeMint to apologize for his schedule change; DeMint said Perry needed to be home.

Romney, who had initially planned to bypass the South Carolina forum, changed his schedule last week to join DeMint, whose backing he enjoyed during his first presidential bid.

While DeMint is tremendously popular here in his home state and with his party's tea party faction, he isn't rushing to publicly pick a favorite this time and has suggested he might not back a candidate in the primary.

That's not to say wooing the tea party is without peril.

After Washington's debt showdown this summer, an Associated Press-GfK poll found that 46 percent of adults had an unfavorable view of the tea party, compared with 36 percent just after last November's election.