In advance of a weekend in which three states will weigh in on the question of who should run against President Bush, the contest's front-runner picked up a key endorsement while his two main rivals took aim at each other.

By all indications, John Kerry (search) had a dominating lead over his Democratic rivals in Michigan, Maine and Washington state. On Friday, former rival Dick Gephardt (search) endorsed the Massachusetts senator — a big win for Kerry in clearing the way toward his party's nomination.

"These are serious times that demand a leader who can go toe-to-toe with George Bush on national security issues, who will defeat George Bush in November, and who is ready to meet the awesome challenges of the presidency," Gephardt said in a statement announcing his endorsement. "That leader is John Kerry."

Recent public opinion surveys also suggest that Kerry has the best chance of defeating Bush, although the president still comes out on top.

A new Fox News poll found that Bush beats Kerry by four percentage points. A month ago, the spread was 22 points — Bush had 54 percent to Kerry's 32 percent.

For more on the campaign, click to view Foxnews.com's You Decide 2004 page.

Meanwhile, North Carolina Sen. John Edwards (search) and retired Army Gen. Wesley Clark (search) ratcheted up their sniping at one another on the campaign trail.

"I think what you're seeing is Wes Clark and Johnny Edwards both trying to be the 'Bubba' candidate — the 'Bubba' Democrat from the South — because if you go forward in the nomination process, one of the things that's going to be key is who has that big block," said Democratic strategist Rich Masters.

The two southerners are stumping in Virginia and Tennessee, choosing to skip this weekend's caucuses and primaries, which offer 228 delegates.

Kerry was set to show up in Tennessee Friday after visiting Michigan, Maine and Washington. Virginia Democrats will meet Saturday night to hear from the candidates.

The most recent public poll in Tennessee, conducted before Kerry's five-state victory Tuesday, showed him leading Clark with Edwards in third. Private polling for the campaigns shows Kerry ahead in Virginia.

"I think John Kerry is a candidate on fire and I think we're heading to a very, very tough, very competitive presidential election," said GOP strategist Roger Stone (search).

Edwards and Clark are both eyeing some of Tennessee and Virginia's 151 delegates to keep Kerry from gaining a win in the South.

And Howard Dean (search) has told his supporters it's Wisconsin or bust for him. He's banking on winning that state in order to breathe new life into his struggling campaign. He also thinks he can win Washington state.

Dean is staying in Wisconsin and told supporters in an e-mail Thursday that he would be out of the race if he didn't score a victory in the primary there.

To do that, he said, he needed to raise $700,000 to launch new TV ads there on Monday.

"We must win Wisconsin," Dean wrote in the e-mail. "A win there will carry us to the big states of March 2 and narrow the field to two candidates. Anything less will put us out of this race."

Apparently, that plea worked. In the 24 hours after the e-mail was sent out, the Dean campaign raised $740,000.

But "Dean has effectively given up in Michigan — he's going to Wisconsin and throwing a Hail Mary pass there, but he's not doing all that well in Wisconsin either," said Dan Klaidman, the Washington bureau chief for Newsweek. "So this may be the end-all for Howard Dean."

A Little 'Blue-Collar Armor' May Go a Long Way

Gephardt wasn't the only prominent lawmaker to back Kerry on Friday. Rep. John Dingell (search), D-Mich. — the longest-serving Democrat in the U.S. House — also endorsed the senator.

"Here's a decorated war veteran who understands war," Dingell told Fox News of Kerry. "Here's a leader in the Senate who has led on education, who has led on foreign policy matters ... who has the national security leadership the country needs, who's led on national defense and who will be a real president."

He joined the likes of Maine Gov. John Baldacci, Sen. George Mitchell, Michigan Sens. Carl Levin and Debbie Stabenow and Michigan Gov. Jennifer Granholm in their support. Michigan offers 128 delegates.

An EPIC/MRA poll taken Feb. 4-5 shows Kerry ahead in Michigan with 62 percent of the vote. The poll of 409 likely Democratic caucus-goers showed Dean with 13 percent, Edwards with 11 percent and Clark with 5 percent. A Detroit News/Mitchell poll of 450 likely caucus voters taken Feb. 3-5 shows Kerry with 52 percent support.

Gephardt's endorsement "is really going to help him [Kerry]. Obviously it helps him in industrial states, it helps him with labor voters," Klaidman said. "It gives him a little blue-collar armor that will help him going forward."

Officials said The Americans for Economic Justice, the alliance of labor groups like the Teamsters, United Steelworkers of America and International Association of Iron Workers that supported Gephardt, could follow.

Labor officials told Foxnews.com last week that they had been hoping to meet with the candidates' campaigns soon "to talk about our issues and how our issues are going to be treated as this campaign moves forward," said Donald Kaniewski, director of legislation and politics for the Laborers International Union of North America, which is part of the alliance.

"That does not guarantee the alliance will make any endorsement ... [but] it's something that's necessary to advance our issue agenda to make sure the things Dick Gephardt offered us, like fair trade, don't get lost in the ongoing debate."

Clark, Edwards Go for the Jugular

While visiting an urban Detroit church Friday, Kerry pledged to continue to support the "unfinished journey for civil rights ... and I intend to be a president who leads you on that march and helps complete the promise."

Clark accused Edwards on Friday, among other things, of voting "against programs to help our nation's veterans" and called for increased health and retirement funding for former members of the armed forces.

"When it came to deciding between the special interests and our veterans, Senator Edwards blinked," Clark said. "He didn't support our veterans."

Visiting a restaurant later Friday, Clark painted Edwards as a Washington insider.

"I'm a leader and not part of the Washington scene," he said. "I'm an outsider. I don't owe anybody anything."

Edwards spokesman Jennifer Palmieri said Clark's charges are a "sure sign of desperation."

"Unfortunately, this is what politicians do when they are losing — they dip into the gutter and throw whatever they find, whether it is true or not," she said.

Clark spokesman Matt Bennett countered, "With his vote against cutting veterans' benefits and now with his campaign's flailing response, John Edwards has proven yet again that he is the product of Washington — a place where you can make bad decisions one day and run away from them later."

Meanwhile, while Edwards was speaking to students at Virginia Tech University on Friday, a couple of students started waving Bush-Cheney signs. Edwards pointed to the signs and said, "that's who's leaving the White House come November."

Edwards later worked the room, but when the students holding Bush-Cheney signs approached him, the senator ignored them.

And Dean launched an all-or-nothing attack against Kerry.

"It's a really clear difference in our record here, a really clear difference in our characters here, and we're going to have this fight, it's gonna be in Wisconsin and we're gonna win it," Dean told supporters in Wisconsin.

Strategy Gone Bad?

But Dean's hope of destroying Kerry with a scorched-earth strategy in Wisconsin may already be backfiring.

Fox News has learned that Gov. Jim Doyle has told friends that he is unhappy about the Badger State becoming a battleground for Dean's brand of negative attack politics and on Friday issued a challenge and a warning to the candidates to stay positive.

In Washington, Dean still draws big crowds but his poll numbers may not be enough to launch him to the top. Even the young Deaniacs seem to be jumping ship.

"A lot of people don't want to view themselves as throwing their vote away in the caucus and a lot of people just assume others won't be supporting Dean," said Andy O'Connell of the Young Democrats at the University of Washington.

Political pundits also said Edwards may be missing a golden opportunity in the Evergreen State, where he's polling at 10 percent. A strong showing on the West Coast, they argue, would go a long way to dispelling the criticism that he only appeals to Southern voters.

Fox News' Major Garrett, Jeff Goldblatt, Catherine Loper, Dan Springer and The Associated Press contributed to this report.