Romney created a stir during his third stop of the day, at an asphalt company garage in the Cedar Rapids suburb of Marion, by telling the crowd, "We're going to win this thing with all of our passion and strength."
He said his team also would "do everything we can to get this campaign on the right track to go across the nation and to pick up other states, and to get the ballots I need, the votes I need, to become the nominee."
A Romney campaign aide quickly told reporters on background that the former Massachusetts governor was referring to the GOP presidential nomination, not the Iowa caucus.
At Romney's stop in Marion, a town near Cedar Rapids, Diana Borash of West Branch said she and her husband, Daniel, decided last week Romney was their choice.
Four years ago, Borash cast her caucus vote for a Democrat, Hillary Clinton, and then voted in the general election for Obama. Since then, she's left the party, saying it has veered too far left.
"Obama has turned America into a country I don't recognize today," the retired 911 dispatch center director said. Borash said she sees Romney as a moderate Republican, offers "the perfect balance" to fix the nation's economic wrongs.
At an earlier campaign stop at a paper warehouse in Dubuque, Rick Hoffman said he still weren't sure he would vote for Romney on Tuesday.
Hoffman said he was still considering supporting Paul. "He has more likeability," he said. But he wasn't sure Paul could go on to win the nomination and the presidency. "That's the whole issue," Hoffman said.
The campaign rolled to a stop around 10 p.m., at a promotional materials warehouse stocked with piles of printed t-shirts and other items located in the upscale Des Moines suburb of Clive.
Among the hundreds filling the huge space was Lee Stine, who planned to deliver a speech for Romney at is Beaverdale caucus meeting. Stine had intended to vote for Bachmann until about a month ago, "when I decided she wasn't going to make it."
Stine said he had liked Bachmann's Iowa background but questioned her ability to run the country as her campaign fell into disarray. Stine said he believes Romney will emerge as the top vote-getter Tuesday. "He's on a roll," Stine said.
Even as late as Monday evening, some voters had not yet made up their minds.
"I don't know much about him," said Karen Jobst of Waukee, who attended Romney's last rally of the day. Jobst said the only candidate she's ruled out supporting at her caucus is Paul. "I don't like the way he comes off," she said.
Still, the warehouse audience erupted into chants of "Mitt, Mitt, Mitt," when Romney started to speak, laughed at his often well-worn jokes, and applauded his criticisms of Obama. They cheered when Romney talked of Obama's first term as his last.
Dozens of television cameras, some from overseas news crews, focused on Romney's speech in front of a giant banner emblazoned with his campaign slogan, "Believe in America."
Even hecklers didn't appear to affect the crowd's excitement.
When several people scattered throughot the warehouse shouted taunts, including "get a job," others at the rally drowned them out by repeating chants of, "Mitt, Mitt, Mitt." Romney smiled and said it was great to live in a country where people could express their opinions.
"Let's get the nomination," Romney said. "Let's become the next president of the United States."
A Romney volunteer said the hecklers were believed to part of the national occupy protest movement, which had threatened to disrupt the caucuses.
Romney's son, Josh, said his father handled the situation well.
"I think he's ready for anything," Josh Romney said. "I don't think he missed a beat."
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