DES MOINES, Iowa - The struggle for votes in Tuesday's Iowa Republican presidential caucuses featured two different fights Thursday.

One involved a top tier of candidates with clear momentum just before the nation's first caucuses. Mitt Romney and Rick Santorum were optimistic Thursday about their prospects. Texas Rep. Ron Paul delivered his somber message to big audiences.

Romney, a former Massachusetts governor, was confident enough to beef up his Iowa schedule, including a stay in Des Moines on Tuesday night to await results. He, Paul, and Santorum, a former Pennsylvania senator and a favorite of Iowa's influential evangelical community, hosted enthusiastic rallies Thursday.

The other squabble featured three candidates who are struggling to stay viable: former House Speaker Newt Gingrich, who has fallen sharply since he briefly was a front-runner this month; Minnesota Rep. Michele Bachmann; and Texas Gov. Rick Perry.

Perry unleashed a radio ad featuring an announcer, "Wink Tax-and-Spend," who hosts a "Wheel of Washington" game show and compares Santorum to a pig because he supported federal budget earmarks for local projects. Perry also has been fighting for the evangelical vote. He suffered a setback in Virginia on Thursday when a federal judge rejected his bid for an emergency court order to require Virginia's Board of Elections to put his name on the March Republican presidential primary ballot.

Bachmann had to convince voters that her campaign is still alive after Iowa State Sen. Kent Sorenson, who had chaired her state campaign, abruptly defected to the Paul camp Wednesday.

Gingrich continued to push for votes on a bus tour around the state. He defended himself against rivals' allegations that he had lobbied in support of the 2003 Medicare prescription-drug law, according to news reports from Sioux City. Conservatives have long been critical of the law, saying it helped the federal deficit balloon. Gingrich said he did not lobby but simply supported the measure.

Tuesday's outcome is difficult to predict. Many voters are still candidate-shopping.

Lyn Watson, an Ames homemaker, voted for Romney in the 2008 caucus but is considering Paul this time. "He feels so strongly about his views," she said, "and he has a good base of people following him." Still, she won't rule out Romney: "Maybe he could work better in Washington."

About 100 of Paul's followers jammed a meeting room at the Hotel Pattee in Perry, where they heard their candidate reiterate his themes of slashing government and reining in U.S. intervention abroad. He denounced sanctions against Iran's nuclear program, saying the Iranian people could interpret the measures as "an act of war."

"I think we're looking for trouble, because we're putting these horrendous sanctions on Iran," Paul said. Iran threatened this week to close the Strait of Hormuz, through which much of the world's oil trade ships, if the West tightens sanctions against it. The U.S. Navy has vowed to keep the strait open.

Romney traveled to Mason City, where he blasted President Obama rather than fellow Republicans.  Responding to a question about his commitment to the state that he long kept at arm's length, Romney said he very much wanted to win it.

"I also want to make sure that I get to the people of New Hampshire and South Carolina and Florida," he said. Those states are next in the GOP nominating process.

Romney urged Iowa voters to look for someone with the best chance of winning the nomination and defeating Obama.

"Who do you think will beat Barack Obama? Who do you think will win the 1,150 delegates it takes to become our nominee?" he asked. "So look at the candidates. Decide who you like and decide also who can become president and can lead this country in a time of challenge."