Romney is helped by the complicated relationships the other top candidates have with Iowa. McCain skipped the state entirely when he ran for president in 2000, and his championing of immigration reform has cost him conservative support. He has, however, built a substantial organization of his own and has 17 Iowa staff members, one more than Romney.

Giuliani, who has nine Iowa staff members, hasn't decided yet if he will participate in the Ames straw poll.

Arthur Sanders, a professor of politics at Drake University in Des Moines, said the GOP establishment in Iowa, after faring poorly in the 2006 election, had "no natural presidential candidate."

"There really was an opening for someone like Romney, and he has certainly filled the gap," Sanders said.

But other Republicans are putting up a fight, notably Thompson and Senator Sam Brownback of Kansas, a favorite of social conservatives, who make up a disproportionate percentage of Iowa caucus-goers. Former Arkansas governor Mike Huckabee, meanwhile, delivered the commencement address at Des Moines University on Saturday.

Romney's opponents aren't wasting any time trying to knock him down, already questioning how strong his Iowa support really is, attributing his bump in the polls to his TV ads, and taking aim at his shifting positions on abortion, immigration, and other issues.

McCain's Iowa chairman, David Roederer, acknowledged that Romney is doing well but questioned whether he has staying power. "You have to make sure you don't peak too early," said Roederer, who chaired the 2004 Bush-Cheney re-election campaign in the state.

Romney returns to Iowa today for one of his "Ask Mitt Anything" public forums, and he and his surrogates will surely spend much of the summer flying in and out of the state. Not all of them will be flying, though: Romney's son Josh has bought a big RV, christened it the "Mitt Mobile," and made plans to visit all of Iowa's 99 counties.

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E-mail: shelman@globe.com