A Republican presidential campaign that has been slow to take shape suddenly snapped into focus Sunday, with an unlikely three-person top tier of former Massachusetts governor Mitt Romney, Rep. Michele Bachmann (Minn.) and the newest entry, Texas Gov. Rick Perry.

After three eventful days — beginning with Thursday’s lively debate in Ames, Iowa, and running through Perry’s formal declaration of his candidacy, Bachmann’s victory in the Ames Straw Poll and former Minnesota governor Tim Pawlenty’s decision to drop out of the race — the Republican Party is now looking at a nomination battle that is far different from the one envisioned at the beginning of the year.

Romney has long been considered the front-runner, albeit one who has stirred only limited passion within the party. But it is the emergence of Perry and Bachmann, who was lightly regarded until she began to demonstrate strong appeal to tea party and other conservative activists, that has greatly changed the race.

Bachmann was not considered a potentially strong candidate when the year began, but her victory in Saturday’s straw poll cemented her status in the upper ranks of the GOP field. Perry long said that he would never run in 2012, but the shifting circumstances of the Republican contest through the first half of the year created a sizable opportunity that he has seized upon.

Bachmann’s victory produced the first major casualty of the race, when Pawlenty, who finished third after Bachmann and Rep. Ron Paul (Tex.), abruptly ended his candidacy Sunday morning.

The busy weekend concluded with Perry and Bachmann sharing the stage at a Black Hawk County Republican Party dinner Sunday night in Waterloo, which is Bachmann’s birthplace.

The dinner provided an early measure of the interest surrounding Perry’s candidacy and displayed the contrasting styles and agendas of the two candidates, with both assuring the audience that they are in the race to win.

Noting that he is a late arrival in the contest, Perry said, “Sometimes it takes me awhile to get into something, like this presidential race, but let me tell ya: When I’m in, I’m in all the way.”

Bachmann was equally emphatic. “People feel it now, the fire, they recognize that Obama can be beat,” she said. “They want to make sure that we don’t just have the other team wearing the other jersey. They want to make sure that they have a champion, a fighter, somebody who’s going to stand up and have guts.”

The Republican race is now a series of likely contrasts, with Romney cast as the establishment candidate who will portray himself as a former businessman who understands how to create jobs and as the candidate who has the best chance of defeating President Obama in November 2012.

Perry will challenge Romney on the economic front and will play on the anti-Washington message that he has been sharpening since Obama took office in early 2009. Bachmann remains the insurgent in the race.

For those Republicans most upset with Obama, she will cast herself as the candidate who has fought him harder than anyone else.

In Perry, Romney faces a potentially formidable governor of a major state who is an economic success story but who is mostly untested nationally. The Texas governor, should he prove to be up to the challenges of handling a bruising presidential campaign, has the ability to stir passions among the party’s conservative base and reach into the GOP establishment for money and endorsements.

But Perry faces his own challenge in trying to fend off Bachmann, who will begin this next phase of the campaign as the favorite of the tea party activists and who has impressed other Republicans with the energy she has brought to the race. Perry has an affinity with fiscal and social conservatives but will have to fight off Bachmann even as he homes in on Romney.

Change in the landscape

Pawlenty’s departure could change the landscape in Iowa. GOP strategists said Bachmann stands as the favorite to win the Iowa caucuses in the winter. But Perry has said he will compete everywhere, and with Romney well-entrenched in New Hampshire, Iowa offers the Texan an opportunity to score an early victory and enhance his chance of winning the nomination.

Romney could reassess, although not necessarily change, his Iowa strategy, advisers say. The former governor skipped Saturday’s straw poll and has shown little interest in competing to win the caucuses. But with Pawlenty out, and Bachmann and Perry going after many of the same voters, a possible opening exists for Romney to make a stronger showing there.

The Romney campaign had anticipated that the straw poll might weaken Pawlenty, whom they considered a potentially strong opponent. They did not expect him to be forced out so quickly. Now, Romney’s team is turning its attention to Perry, suggesting that he will have to prove his mettle in Iowa and everywhere else, starting with a trio of debates next month.

How Perry performs in those debates will help determine his readiness for a campaign that came upon him suddenly and for which he has had only minimal time to prepare. But many Republicans say that, despite his late entry, they consider him a potential long-distance runner. As one put it Sunday, “Nobody thinks he’s another Fred Thompson.”

That was a reference to the disastrous campaign waged by the former Tennessee senator, who entered the 2008 presidential race about this time four years ago and who never made a mark.

As Romney returns to the campaign trail Monday in New Hampshire, he plans to continue his assault on Obama and will highlight his private-sector experience and business know-how, drawing a subtle contrast with Perry. The Texas governor has spent several decades in elected office, and in interviews Sunday, Romney strategists described Perry as a career politician.

‘Politics is a contact sport’

Ray Sullivan, the Perry campaign’s communications director, said any criticism from rivals will be met with a sharp counterattack. “We will certainly and vigorously defend the governor’s record and vision,” he said. “Politics is a contact sport, and it certainly is a contact sport in Texas, and we’re prepared.”

During Romney’s visit to Iowa last week, reporters asked him about Perry’s entry into the race and whether the Texan had stronger credentials on job creation. Romney did not directly speak to Perry’s record but drew a clear comparison when he said: “I think I’m the right guy to be the Republican nominee for president, in part because I’ve spent 25 years in the private sector and I know how the economy works.”

As the news that Pawlenty was dropping out spread Sunday morning, Romney called the former governor, and they had what a Romney aide described as a “good conversation.” Meanwhile, some of Romney’s advisers and key supporters were reaching out to Pawlenty’s financial and political backers to gauge their willingness to support Romney.

On Sunday morning, Bachmann appeared on all five public affairs show, basking in Saturday’s victory while deflecting tough questions as the media scrutiny on her record intensified.

On NBC’s “Meet the Press,” anchor David Gregory asked Bachmann a flurry of questions about her stance against raising the federal debt ceiling, the roles that faith and sexuality would play in her administration, and her ability to win support from independent voters in a general election against Obama.

“All of these kinds of questions aren’t what people are concerned about right now,” she said.

CNN’s Candy Crowley asked Bachmann whether her stance against any compromise during the debt debate put her outside the political mainstream. Bachmann said: “Oh, goodness, absolutely not.”

Perry began his second day as a candidate in New Hampshire, where he walked through a Manchester fair with his cowboy boots and Texas swagger. Posing for pictures, he greeted prospective voters with “Howdy, y’all.”

When a reporter asked whether he was Romney’s “worst nightmare,” Perry signaled that he would run a tough race. He said there would be “a lot of time to discuss Governor Romney’s record.”

“I hope I’m not anybody’s worst nightmare,” Perry said. “I hope I’m a very worthy competitor.”

Asked whether he was “too Texas” for a general election, Perry said: “Aww . . . I don’t think so. You know, we’re not all carbon copies in Texas.”

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Staff writer Nia-Malika Henderson in New Hampshire contributed to this report.