Des Moines, Iowa (CNN) -- Iowa Gov. Terry Branstad nicely summed up the stakes of the Ames Straw Poll this week during a television appearance.

"If you're not the top three here, your chances of getting elected are not very good," said Branstad, a veteran observer of Republican politics in the state.

The consensus among Iowa GOP insiders is that Minnesota Rep. Michele Bachmann, former Minnesota Gov. Tim Pawlenty and Texas Rep. Ron Paul will take the top three positions in Saturday's vote.

The open question is who will finish where.

The straw poll is hardly predictive. In 2007, former Massachusetts Gov. Mitt Romney won the vote, but his closest rival in the state, former Arkansas Gov. Mike Huckabee, ultimately won the Iowa caucuses and dealt a fatal blow to Romney's candidacy.

Since the contest began in 1979, only one Republican has won the straw poll and gone on to occupy the Oval Office: George W. Bush.

But in past election cycles, the vote, a fundraiser for the Iowa Republican Party, has weeded out candidates who have staked their candidacies on Iowa but struggled to generate grassroots enthusiasm.

Nine announced candidates are on the straw poll ballot, but two of them -- including Romney and former Utah Gov. Jon Huntsman -- are skipping the contest. Huntsman is skipping the caucuses completely, while Romney's advisers are carefully watching the state and could pounce in the coming months if they see an opening.

Former House Speaker Newt Gingrich is on the ballot, too, but his cash-strapped campaign will not have a formal presence at the straw poll.

Michigan Rep. Thaddeus McCotter shelled out thousands of dollars to reserve campaign space outside the straw poll venue, but he is not expected to be a major factor in the vote.

Republicans will also be watching to see how many write-in voters Texas Gov. Rick Perry picks up. He will be announcing his candidacy on the same day in South Carolina, prompting some grumbling among Iowa Republicans.

Meanwhile, here are five candidates who must do well in the Iowa caucuses next year and are counting on a strong performance at Ames to keep their campaigns afloat.

MICHELE BACHMANN

Bachmann is the Iowa front-runner. She is at or near the top of most Hawkeye State polls, thanks to the passions she has stirred among tea party activists and social conservatives who make up a large part of the caucus electorate.

But there are questions about how strong her organization in the state is and whether she can compete with Pawlenty's respectable ground game.

Like Huckabee in 2007, though, Bachmann has a natural appeal to evangelicals and home school activists who tend to show up at political events like straw polls.

TIM PAWLENTY

Pawlenty has a platoon of smart political operatives in his corner and is thought to have the best ground game in the state. But despite planting an early flag in Iowa and improving his performance on the stump in recent weeks, the genial Midwesterner remains stuck in single digits in state polls.

His aggressive tack in Thursday's presidential debate, in which he directly challenged Bachmann's fitness for national office, was intended to change that. But it's not clear he did enough to knock his top Iowa rival from her perch.

The question for Pawlenty is whether organization can trump enthusiasm. In the past, it has. The straw poll is a test of how well each campaign can organize its supporters and get them to the ballot box.

It can turn into an expensive proposition: Campaigns purchase hundreds of tickets and bus voters into Ames from across the state. Once there, they are enticed with free food, music, giveaways and speechifying.

Pawlenty has struggled to define a rationale for his candidacy. He must finish in first or second place and send a message to his supporters (and the media) that his campaign can soldier on through the fall and winter.

RON PAUL

Paul is the Harlem Globetrotter of straw poll contestants. He never loses.

And that's both a blessing and a curse.

His straw poll wins over the last four years at various conservative gatherings are a testament to the devotion of his libertarian-leaning followers and their ability to out-organize and out-hustle the competition.

And with the economy in the doldrums and grassroots conservatives fired up, Paul's limited government message this year has even more resonance among fiscal conservatives than it did during the 2008 cycle.

But when you win as much as Paul, expectations are high. These days, political observers and members of the media take his straw poll wins for granted.

RICK SANTORUM

There have been some whispers that Santorum, who has spent more time in Iowa than any other candidate but remains near the bottom of most polls, might sneak up on Pawlenty on Saturday.

His chances may have been helped by a respectable debate performance on Thursday, when he scored loads of free airtime by attacking Paul on foreign policy.

Still, there are lingering questions about the strength of his organization in the state. If Santorum finishes in the top three, it would be a welcome surprise for his campaign.

HERMAN CAIN

Cain, a businessman and former radio host running on his outsider image, is fading after a strong early start to the campaign.

He has tried to manage expectations for the straw poll but recently told a Des Moines audience that he needs to finish in the top three. Anything less, he said, would compel him to "evaluate" his campaign.