The way Tim Pawlenty is racing around Iowa this week is proof of how much the former Minnesota governor has riding on the state GOP's presidential straw poll next month.

Pawlenty pulled up to the Coralville Public Library in the blistering midday heat Monday in an RV plastered with his name and picture, a straw poll registration website address and the slogan "America's future begins in Iowa."

"This is going to be a defining moment," the former Minnesota governor told 50 GOP activists, glistening with perspiration in the cool of the library's basement. "This will have a lot to say about the shape of the race. It will be kind of the opening salvo in the race. And Iowa is in the position to be the launching pad."

The sprint is under way for the straw poll, a make-or-break moment for Pawlenty, who has spent 18 months networking in Iowa but has registered in the single digits in this pivotal early-voting state.

Pawlenty needs a strong performance at the Aug. 13 event at Iowa State University to show his slow-to-catch-fire campaign has momentum. He's scheduled to hit 18 cities in 13 Iowa counties this week, covering an estimated 700 highway miles in his rolling campaign billboard.

Pawlenty's campaign also has reserved $200,000 in television advertising time in the Des Moines media market, the biggest ad buy of any candidate in any state of the 2012 campaign so far. Pawlenty, who has been advertising in Iowa since last month, plans to begin airing a new ad in the coming days.

The straw poll is an Iowa Republican Party fundraiser in Ames, where thousands of GOP activists converge on Iowa State University's Hilton Coliseum to weigh in on the presidential field. Beating expectations in Ames can boost a candidate's fundraising and provide buzz from the horde of media who flock to the event. Falling short can cripple a campaign, or abruptly end it.

The straw poll is a chance for Texas Rep. Ron Paul, who has signaled a more concerted Iowa effort than four years ago, to crack the top tier in Iowa. It can also extend _ or cut short _ campaigns by lesser-known candidates such as former Pennsylvania Sen. Rick Santorum.

It would be a blow to Pawlenty to be beaten badly at the straw poll, especially considering the leading candidate in most national GOP polls, former Massachusetts Gov. Mitt Romney, and likely candidate Rick Perry, the Texas governor, will not be participating.

But Pawlenty is not the only one facing high expectations at the straw poll.

Minnesota Rep. Michele Bachmann shot to the top of polls in Iowa last month and has recently been holding "Join me in Ames" events in Iowa to sign up straw poll supporters.

She campaigned in seven Iowa cities over the weekend and is scheduled to campaign in the state again Wednesday.

Bachmann's upbeat and vocal appeal to tea party activists and evangelical conservatives has ignited passion in her early campaign. She needs to show at the straw poll that she can attract votes.

Pawlenty struggles to spark enthusiastic ovations, although he gets favorable reviews from activists for his blue-collar upbringing and as an experienced governor in a political swing state.

But Pawlenty, who says his campaign is more about substance than spitfire, has ratcheted up his tone lately, especially when challenging President Barack Obama.

"He was in the United States Senate long enough to have a cup of coffee before it got cold," Pawlenty said, his voice rising, in Coralville. "And then we put him in the Oval Office, the most important position in the free world _ someone who hadn't run anything, hadn't done anything."

Pawlenty has tried to tamp down straw poll expectations in recent weeks, as Bachmann has risen sharply in polls of Iowa GOP caucus-goers. But his campaign aides say it represents the first chance to show he can close the deal with influential activists, which has been a challenge for him in a field that has yet to gel.

Although one Pawlenty staffer reported signing up eight for the straw poll at the Coralville event, getting some to commit to turning out on a Saturday was a difficult task.

"He's in my top two or three. I like him, what he stands for and his experience," said Iowa City Republican Paula Lynch, who calls Pawlenty a finalist for her support. "But I don't know if I can make it to the straw poll. My husband would have to go with me, and I don't know who I'd vote for at this point if I did go."