Updated

Front-runner John Kerry (search) said Friday he is prepared for an onslaught of criticism from the Republican Party and is ready to fight back as he moves closer to the Democratic nomination for president.

"We've seen evidence. We know exactly where these guys are gonna go, and I'm ready for it," Kerry told radio broadcaster Don Imus. "I've been at this for a while, Don, and I've been through some tough races. I've been pretty well, you know, vetted and examined from one side to the other. And I think that they're in for a surprise. I'm going to fight back. I am a fighter, and I'm ready to fight back."

In Nevada, which holds caucuses Saturday, GOP Chairman Ed Gillespie (search) told Republicans Thursday night that Democrats were preparing to run "the dirtiest campaign in modern presidential politics."

"This is because they don't want a debate on the issues, and they don't want to run on Senator Kerry's record," Gillespie said in prepared remarks. "I guess I can't blame them for that."

Kerry traveled to Madison, Wis., on Friday to campaign with Wesley Clark, who was expected to endorse Kerry. Clark dropped out of the race Wednesday, and the Massachusetts senator hopes to make Clark's voters his own when he clashes with Sen. John Edwards and Howard Dean in Tuesday's Wisconsin primary.

There are 72 pledged delegates at stake in Wisconsin, and polls make Kerry the favorite. His support increased from 41 percent in a survey taken last weekend to 53 percent after Clark's withdrawal, according to a poll released Thursday night by the American Research Group. John Edwards was at 16 percent and Howard Dean at 11 percent with 16 percent undecided.

Kerry already has 539 delegates, according to an Associated Press count, compared to 182 for Dean and 166 for Edwards. It takes 2,161 delegates to win the nomination for president.

Kerry said Friday he would not discuss questions about President's Bush's service in the National Guard. "It's not my record to comment on. I'm not going to pay any attention to it," he told Imus.

Asked about a photograph showing him sitting near actress Jane Fonda at an anti-war rally in 1970, Kerry said he protested the war after he had served in Vietnam and considered doing so a measure of his character.

Fonda has been criticized for decades for her opposition to the Vietnam War, particularly for traveling to North Vietnam in 1972, at the height of the war, and posing in an anti-aircraft gun.

"I disagreed, like everyone else in America, with the choice she made at that point in time. I thought it was terrible," Kerry said on the Imus program. "We just move on, Don. We're 30 years beyond that. I think people are interested in the future."

Edwards, who has won only one primary, made clear that he intends to remain in the race regardless of his showing in Wisconsin. After spending time in the state Thursday, he flew to Los Angeles to raise money.

His schedule for Friday was a copy — in Wisconsin in the morning, then back to Los Angeles for fund raising.

Edwards, of North Carolina, has refrained from the type of attacks that other candidates have used in the race, and in an interview with The Associated Press, said the decision has helped him.

"The American people are tired of the same old politics that they've seen for so long, the attack politics," he said.

By contrast, Dean has become increasingly critical of Kerry in recent days as he looks for an upset in Wisconsin.

The former Vermont governor, winless to date in the primary season, campaigned with his wife, Judy, during the day, using health care to emphasize his campaign's call for change in the way business is done in Washington.

At a town hall meeting in Oshkosh, Dean said lobbyists, pharmaceutical companies and corporate health care all block efforts to hold down costs and expand coverage.

"Special interests in Washington stop real change every time," he said. "The process is broken. In order to change America we have to change Washington."

Dean is the former front-runner in the race, and a nursing school training dummy might seem a curious campaign prop. But he leaned over the dummy nonetheless, touching the arm as if feeling for a pulse.

"I don't like that breathing pattern very much," Dean said to his wife — like him, a physician.