McCain's embattled campaign quickly followed Giuliani's lead, perhaps hoping to dilute the impact of a potential Romney win at the straw poll.
The name of former House Speaker Newt Gingrich will not appear on the ballot -- even though he is mulling an '08 bid. Fred Thompson isn't showing up at Ames poll either, but he will begin campaigning in Iowa on Aug. 17.
For second-tier candidates, the straw poll is a double-edged sword. It's all about expectations: A strong showing could legitimize their candidacy and boost their chances of doing well in the January Iowa caucuses, but a poor finish could be disastrous to any campaign that's having trouble catching on.
"If I don't finish first or second, I'm not going to continue," Tommy Thompson, the former governor of Wisconsin, said Tuesday on MSNBC. "If I don't come in first or second, I'll say I tried, gave it my all, and I'll go home to Wisconsin."
In a last-minute attempt to erode Romney's strong support in Iowa just days before the Iowa straw poll, Huckabee targeted the front-runner Thursday, warning that supporting Romney would leave the party vulnerable to Democratic charges of flip-flopping that could endanger GOP chances of winning the White House in 2008.
"Let's assume everything is hunky-dory with his views now," Huckabee told WashingtonPost.com. "What's problematic is that it does represent a dramatic shift and the obvious thing that a Democrat[ic] opponent will do to him is to say he shifted once, will he shift again?"
The timing of the attack speaks to the importance Huckabee is placing on the straw poll.
"It shows that folks are willing to drive across the state, show up and cast a vote," Huckabee told ABC News Sunday following the Republican debate. "These are people who have to purposely come to Ames and say, 'We like Mike Huckabee.'"
Republican strategists agree that Huckabee needs to do well at the poll.
"If Huckabee doesn't do well, he may have to drop out," Reed said.
Other second-tier candidates are downplaying its outcome.
"It's our preseason game," said Bay Buchanan, a top adviser to Rep. Tom Tancredo, R-Colo. "This is a test of our team in Iowa to clarify our weaknesses and see where we are strong."
The latest ABC News/Washington Post poll released last week had 26 percent of likely Republican Iowa caucus-goers supporting Romney, with Giuliani and Fred Thompson -- who has not yet formally announced his candidacy or campaigned in the state -- at 14 and 13 percent, respectively. McCain and Huckabee tied with eight percent support each.
However, the straw poll is nothing like a scientific poll. Only 20,000 to 40,000 Iowans usually show up, and most of them are bussed in by campaigns. So candidates must vie for votes in unorthodox ways, offering food, music and a good time in exchange for votes.
"It's going to be about a 95-degree day, it's going to be hot and humid," McCormick said, noting that the straw poll must compete for attendance with the state fair in Des Moines. "This is not the way most people want to spend their Sunday, so they have to have some incentive to come and enjoy the day."
Iowa's Des Moines Register reported this week that supporters of Ron Paul, R-Texas, a long-shot presidential candidate, have already questioned the integrity of the voting procedure -- something political observers have dismissed.