Rep. Michele BachmannMichele Marie BachmannBachmann won't run for Franken's Senate seat because she did not hear a 'call from God' Billboard from ‘God’ tells Michele Bachmann not to run for Senate Pawlenty opts out of Senate run in Minnesota MORE (R-Minn.) and former Minnesota Gov. Tim Pawlenty are running hard in Iowa in the lead-up to Saturday’s Ames Straw Poll.

Both have much to lose if they underperform expectations and don’t win or finish a close second in the state. Rep. Ron Paul (R-Texas) is also expected to do well, further increasing the pressure on the Minnesotans.

The straw poll is the first major test of presidential candidates’ organizations in the early caucus state, and may be their last chance to prove their mettle if Texas Gov. Rick Perry decides to launch a presidential campaign. (He is not on the straw poll's ballot.)

And for some contenders, there may be pressure to drop out of the contest after the results are in. Both former House Speaker Newt Gingrich (R-Ga.) and former Sen. Rick Santorum (R-Pa.) have struggled for attention and financial support. Depending on how they do Saturday, some observers could be writing their campaigns' obituaries. (Gingrich will attend the straw poll but is not a paying participant, meaning he won't be speaking.)

But it's Bachmann and Pawlenty who have banked on Iowa to give their campaign momentum. Both candidates are making big pushes in the state this week.

Bachmann will campaign through Iowa throughout the week, with 14 announced rallies, town halls and church visits between this past weekend and the straw poll. She will also participate in a Thursday debate with all of the other major candidates including former Massachusetts Gov. Mitt Romney, who is skipping the straw poll.

Pawlenty will also spend much of the next week in the state. The former governor will meet with Christian conservatives and others throughout the week, and appear at the Iowa State Fair on Friday, the day between the debate and straw poll.

Meanwhile, Paul is scheduled to arrive in the state on Tuesday with his son, Sen. Rand PaulRandal (Rand) Howard PaulDem wins Kentucky state House seat in district Trump won by 49 points GOP's tax reform bait-and-switch will widen inequality Pentagon budget euphoria could be short-lived MORE (R-Ky.).

According to sources, many Republicans who plan to attend the straw poll are still undecided on their candidate, which is very unusual this close to the event. That makes Thursday's debate even more important, as it is the largest event ahead of the straw poll itself.

Bachmann’s biggest concern is managing the expectations game. While she has rocketed into the lead in polls of Iowa Republicans, her ground game is still playing catch-up. To keep her front-runner status and the free media and fundraising advantages it entails, she will need to finish at or near the top in the poll.

Her campaign has tried to downplay expectations, arguing that because she didn’t start campaigning in the state until this summer she should not be expected to do that well. But the state has been the focus of her campaign since she announced her candidacy in her childhood hometown of Waterloo, Iowa. She has spent much time there in the last two months, purchased numerous television ads, and is spending heavily on the straw poll, offering a petting zoo, performances by country acts including Randy Travis and free barbecue.

Republican operatives in the state said she needs a first-place finish.

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“Because her relative visibility on the campaign to this point is high, she has to do very, very well in the straw poll in order to maintain her standing in the polls,” said former Iowa Republican Party Executive Director Dee Stewart, who ran the 1999 Straw Poll. “If Congresswoman Bachmann does not have a very strong finish, her poll numbers will begin to slip.”

Pawlenty also needs a strong showing and has invested much time in the state. He has spent almost double the time in Iowa as Bachmann and has a large team of paid staff in the state including Sarah Huckabee Sanders, who helped her father, former Arkansas Gov. Mike Huckabee, to a surprise second place finish in the 2007 straw poll. Huckabee ultimately won the 2008 Iowa caucuses.

The former governor's campaign will treat its supporters to musical acts, free Dairy Queen and barbecue.

He badly needs to change perceptions that he is a candidate that many Republican voters like but don’t love.

“You shouldn’t take his struggles in Iowa as ‘Iowans don’t like him,’” said former Iowa Republican Party Political Director Craig Robinson. “The question is: Can he excite people enough ... to spend a full day and get on a bus for this guy?”

Without a strong finish, Pawlenty will struggle to raise the money needed to run a top-tier campaign as potential donors look around for a proven candidate.

Paul has proved that he can win straw polls – he won the Republican Leadership Conference poll in June and the Conservative Political Action Conference’s earlier this year. Iowa is a much larger event that the other candidates take more seriously, and Paul can’t rely on fervent followers from other states to come to his aid because the poll is closed to non-Iowans. But observers say his ground game is somewhat improved from 2008, when he finished fifth after doing little organization. He could be a major player on Saturday.

If Paul does pull off a second-place finish, it could spell major trouble for whoever is behind him. Robinson described third place as “the widow-maker,” and pointed out that both then-Sen. Sam Brownback (R-Kan.) in 2007 and former Sen. Elizabeth Dole (R-N.C.) in 1999 couldn’t get their campaigns on track after finishing third.

-- This story was last updated at 11:59 a.m.