AMES, Iowa (AP) -- The 2012 Republican presidential race heated up Saturday as latecomer Texas Gov. Rick Perry formally announced his candidacy and Iowans weighed in for the first time on their expanding field of presidential hopefuls, picking U.S. Rep. Michele Bachmann as their top choice for the party's nomination.

Together, the events were certain to reshuffle the race to face President Barack Obama who has become increasingly vulnerable because of the sputtering economic recovery. Nearly a dozen Republicans are seeking the chance to challenge Obama in November 2012 for the leadership of a country facing a recent downgrade in its credit rating, high unemployment and Wall Street tumult.

Bachmann _ a favorite of the small government, low tax tea party movement with a following among evangelicals who make up the Republican base in Iowa and elsewhere _ got more than 28 percent of the 17,000 votes cast in the nonbinding straw poll. It provides clues about each candidate's level of support and campaign organization five months before the Iowa caucuses kick off the presidential nomination season.

``We are going to make Barack Obama a one-term president,'' Bachmann declared to cheers on the campus of Iowa State University during a daylong political festival. A few hours later, after learning she had won the straw poll, she said: ``This is the very first step toward taking back the White House!''

U.S. Rep. Ron Paul of Texas, who has support among libertarian-leaning voters, came in a close second. Former Minnesota Gov. Tim Pawlenty was looking for a strong showing to boost his struggling campaign, but fared a distant third, raising questions about the future of his candidacy.

From Iowa to South Carolina on Saturday, Republican candidates used their perches before party activists in two critical early presidential nominating voting states to castigate the Democratic incumbent and offer themselves as the answer to an ailing America.

In Charleston, South Carolina, Perry, the longest-serving governor in the nation's second largest state delivered a withering attack on Obama in his first speech as a full-fledged presidential candidate to a gathering of conservative bloggers.

He criticized ``broken'' Washington, which he said mismanaged its finances and levied undue regulation on people's lives and businesses. He slammed the deal struck by Obama and congressional leaders last week to raise the debt ceiling; a downgrade of the nation's credit rating by a leading ratings agency came just days later.

``This is just the most recent downgrade,'' Perry said. ``The fact is for nearly three years President Obama has been downgrading American jobs. He's been downgrading our standing in the world. He's been downgrading our financial stability. He's been downgrading our confidence, and downgrading the hope for a better future for our children.''

Perry's nationally televised announcement of his candidacy in the first-in-the-South primary state of South Carolina came _ not coincidently _ on the same day as the Iowa straw poll, and his entrance in the field capped a remarkable turn of events.

As recently as a few months ago, Perry foreswore any interest in running for president.

He reversed course after it became clear that the Republican establishment wasn't rallying around any single candidate and that many in the party's base had reservations about their choices, including former Massachusetts Gov. Mitt Romney, until now the front-runner in early polls four years after losing his first presidential campaign.

Perry is viewed as one of the few Republican candidates who can unite disparate elements of the Republican coalition. He has the backing of many supporters of the small government, low tax tea party movement, and is popular among social conservatives for his opposition to abortion and gay rights. He is also an evangelical Christian and hosted a prayer rally last weekend in Texas that drew thousands of attendees.

Even before he officially entered the race, some polls of Republicans showed Perry running only a few percentage points behind Romney and well positioned to emerge as the top alternative from the party's conservative wing to the former Massachusetts governor.

Perry can go head-to-head with Romney on the issue of job creation, a key issue in the upcoming campaign. Through three terms as Texas governor, Perry has overseen significant job growth in his state while working to keep taxes low. Romney has touted his extensive background as a businessman to persuade voters he can turn the economy around.

At the same time, Perry can challenge Bachmann for support among social conservatives and tea party activists, but can also cite his executive experience as Texas governor, which the three-term Minnesota congresswoman lacks. The party's staunchest conservatives are wary of Romney's past support as Massachusetts governor for gay and abortion rights and a health care reform package used by Obama as a model for legislation that Republicans loathe. Evangelical Christians look askance at Romney's Mormon faith.

Perry has spent the past few weeks assembling a national finance team supporters say could rival Obama's. The president is on track to match or exceed the record-breaking $750 million he raised in 2008.

But Perry has never run a national campaign before, and his deeply conservative views may not sit well with voters in some parts of the country. His candidacy will also be a test of whether Americans are ready to elect as president another Texas governor, so soon after former President George W. Bush left office with record low approval ratings.

In Ames, Iowa, thousands of Republican activists gathered at Iowa State University for the straw poll that officially serves as a fundraiser for the state party. They ate barbeque and listened to live music under tents on the campus while milling with candidates who delivered speeches inside the university's coliseum, trying to sway still undecided Republicans.

The straw poll, an every-four-years vote by thousands of Republican activists, can shape the race for the months ahead by providing winning candidates with a boost. Poor showings usually force some candidates, mostly those who are not well-known and are struggling to raise money, to abandon their bids. That could happen this year, too.

With the victory, Bachmann is all but certain to get a jolt of momentum just as Perry seeks to infringe on her base of tea party and evangelical support. She also made clear that she has a strong get-out-the-vote operation and a wide volunteer base in a state whose caucuses require those elements.

Bachmann, an Iowa native who has shot to the top of polls in the leadoff caucus state since entering the race, has spent weeks meeting privately with ministers, who for years have formed a useful Republican political network in Iowa. Pastors helped former Arkansas Gov. Mike Huckabee win the 2008 caucuses, and may have done the same for Bachmann on Saturday.

The results were a setback for Pawlenty, who has ranked low in the polls and was seeking to prove he is a viable candidate. He has struggled to gain traction against an unexpectedly strong challenge from Bachmann in Iowa, a state critical to both of their candidacies.

``We have a lot more work to do,'' Pawlenty said, making clear he wasn't dropping out despite a disappointing finish. ``We are just beginning and I'm looking forward to a great campaign.''

Paul, for his part, was hoping that his surprisingly strong second place showing would convince Republicans that he was more mainstream than not in his second shot at the Republican nomination. He dismissed his fellow Texan Perry as a ``super-establishment candidate.''

Former Pennsylvania Sen. Rick Santorum was fourth in the straw poll, followed by businessman Herman Cain. Perry _ who wasn't on the ballot but was written-in by supporters _ came in sixth, just ahead of Romney, who did not compete in the straw poll. Also on the ballot but barely registering support: former Utah Gov. Jon Huntsman and former U.S. House Speaker Newt Gingrich of Georgia.

From South Carolina, Perry traveled to New Hampshire, where Romney is favored in the state that holds the first primary in the presidential campaign.

``I intend to compete for every vote in every state,'' he said, speaking to roughly 100 supporters gathered next to the backyard pool of a state representative. ``This isn't a strategy just to go work in a few places. I'm going to be all across this country.''

His matchup with Bachmann begins Sunday when they both appear at the same county Republican event in Iowa.

Obama was to begin a three-day bus tour on Monday of Minnesota, Iowa and Illinois, three Midwestern states critical for his re-election.

Obama campaign spokesman Ben LaBolt released a statement slamming Perry before his speech had even concluded _ a move that signaled the campaign views Perry's candidacy as a threat.

``In a Republican field that has already pledged allegiance to the tea party and failed to present any plan that will benefit the middle class or create the jobs America needs to win the future, Gov. Perry offers more of the same,'' LaBolt said in a statement.