AMES, Iowa — At his final campaign rally before today's straw poll of Iowa Republicans, GOP presidential candidate Mitt Romney sure sounded like he'd already won.

"It's going to be a shot heard around the world. People are going to know what this campaign is all about," Romney told a crowd of several hundred cheering friends and family members Friday night. "Let's go on to win the White House."

Romney is widely seen as the favorite among the 11 candidates whose names appear on the ballot for the non-binding poll, which is a fund-raiser for the Iowa Republican Party.

His two chief competitors for the GOP nomination, former New York City Mayor Rudy Giuliani and Arizona Sen. John McCain, are skipping the daylong event at Iowa State University's Hilton Coliseum.

But Giuliani made campaign stops in Iowa this week, fueling speculation he'll do better than expected in the straw poll. And actor and former Tennessee Sen. Fred Thompson's name is on the ballot, even though he has yet to formally announce he's running for president.

Another potential GOP presidential candidate, former House Speaker Newt Gingrich, told Iowa Public Television that Romney's campaign "will be over if he doesn't come in a substantial first." Gingrich is not on the straw poll ballot.

Romney's campaign put out a news release Friday warning that there could be a lower turnout today than in 1999, when now-President Bush was the national front-runner. Although Romney is seen as the front-runner in Iowa, he trails in national polls behind Giuliani, McCain and sometimes Thompson.

While the results of the poll will have no effect on the Iowa caucus vote now expected to be held as early as mid-December, a poor showing could spell the end for some campaigns. Former Wisconsin Gov. Tommy Thompson told reporters again today he'll drop out unless he comes in first or second.

Thompson said he couldn't afford to keep up with Romney's spending in Iowa, especially on television commercials. The Romney campaign has declined to say how much the Iowa campaign is costing, but the Washington Post reported Friday that a Democratic source estimated Romney has spent nearly $5 million on television commercials and other campaign materials.

"He's spent a lot of money. I spent $1 for every $10 he's spent. I've got one person for every 10 people he's got in Iowa," Thompson told reporters after delivering a speech at the Iowa State Fair in Des Moines. "I'm working harder."