The front-runner by far, Kerry fashioned his latest victories by outsized margins on Saturday.
The Massachusetts senator's share of the vote in a multi-candidate field hovered at 50 percent in both Washington and Michigan.
Howard Dean had his best showing of the campaign season. He finished second in Washington with 30 percent of the vote and was battling for runner-up status in Michigan. But that was cold comfort for the former Vermont governor, whose once promising campaign unraveled further when the head of a major union withdrew his support.
Democratic officials said Gerald McEntee, head of the American Federation of State, County and Municipal Employees, delivered the news to the former front-runner during a meeting in Burlington, Vermont. It was a fresh blow for Dean, who has been shut-out in the primary season to date.
With 80% of precincts in Washington reporting their results, Kerry had logged 49% of the vote. In second place was Dean, who trailed the senator by 18 percentage points. Ohio Rep. Dennis Kucinich had 8% of the vote, and Sen. John Edwards trailed him by one point with seven percent.
Returns from 15 percent of Michigan's caucuses showed Kerry with 57% support. Edwards had 15 percent and Dean 14 percent.
A Michigan party official speaking on condition of anonymity told the Associated Press that almost-complete returns showed Kerry with 55 percent, Edwards and Dean at 15 percent, and Sharpton winning 10 percent.
Eager to show strength in all regions of the country, Kerry campaigned through Southern battleground states during the day on Saturday.
John Edwards, Wesley Clark and Howard Dean held out minimal hope for the day's contests, aiming instead for states still ahead on the campaign calendar.
Michigan's caucuses permitted voting via the Internet as well as by mail or in person. Mark Brewer, the party's executive chairman, said an estimated 40,000 to 50,000 online ballots had been received by midday.
The party also decided to keep caucuses in Detroit open two hours later after receiving complaints from supporters of Dean and Edwards that voting sites had been closed or moved.
A CBS News poll of Michigan caucus absentee (Internet or mail) voters showed that on Election eve, Internet voters were younger, had higher incomes, and were backing Kerry.
Kerry led the Democratic field among both those voting by mail and online, with Howard Dean 16 points behind, the CBS News Election and Survey unit said.
The Michigan Democratic Party received more than 100,000 requests for absentee ballots.
Michigan had 128 delegates at stake in caucuses, and Washington offered another 76.
Maine, with 24 delegates at stake, was holding caucuses on Sunday.
Turnout in Washington and Michigan was described as heavy Saturday.
CBS News Correspondent Cynthia Bowers says, "That so many voters showed up in two caucuses that were all but determined should fire a warning shot across the bow of the Republican Party that these voters will be back come November."
Kerry paid scant attention to his Democratic rivals Saturday, focusing instead on the Republican in the White House.
He vowed to aggressively counter Republican critics, drawing a stark contrast between his party and the GOP. "They're extreme. We're mainstream, and we're going to stand up and fight back," he said.
The Massachusetts senator, under fire from White House allies, sought to assure Democrats that he wouldn't repeat mistakes of 1988 Democratic nominee Michael Dukakis, who responded cautiously to George H.W. Bush's assertions that he was a Massachusetts liberal.
"This week, George Bush and the Republican smear machine have trotted out the same old tired lines of attack that they've used before to divide this nation and to evade the real issues before us.
"Well, I have news for George Bush, Karl Rove, Ed Gillespie and the rest of their gang: I have fought for my country my whole life. I'm not going to back down now," Kerry, a decorated Vietnam veteran, said in remarks delivered Saturday night to Virginia Democrats in Richmond.
Rove is President Bush's top political adviser. Gillespie, head of the Republican Party, has borrowed from the 1988 playbook to label Kerry a Massachusetts liberal with a "long record in the Senate is one of advocating policies that would weaken our national security."
"This is one Democrat who's going to fight back, and I've only just begun to fight," he said. "George Bush, who speaks of strength, has made America weaker - weaker economically, weaker in health care and education. And the truth is George Bush has made us weaker militarily by overextending our forces, overstraining our reserves, and driving away our allies."
Earlier, Kerry said he'll campaign against Mr. Bush in the South, dismissing Republican assertions that he is too liberal and out of touch to win in Dixie.
"This administration is busy trying to paint everybody else as out of touch, out of synch, somehow out of the mainstream," Kerry said at a Nashville university. "But let me tell you something: I'm not worried about coming down South and talking to people about jobs, schools, health care and the environment. I think it's (the president) who ought to worry about coming down here."
Clark and Edwards were pinning their hopes on Tuesday's primaries in Virginia and Tennessee while Dean is making a last stand in Wisconsin, which votes a week later.
Kerry has won seven of nine primaries and caucuses held to date, losing only South Carolina to Edwards and Oklahoma to Clark last week.
Kerry's rivals soldiered on Saturday.
Edwards, a first-term senator from North Carolina, made it sound like additional defeats - even in Virginia, Tennessee and on Feb. 17 in Wisconsin - would not deter him.
"This is very much for me a long-term process. It's a war of attrition," he told reporters while campaigning at the University of Memphis. "I'm in it until I'm the nominee."
While concentrating his efforts in the South, Edwards also flew to Wisconsin during the day to accept the endorsement of the Union of Needletrades, Industrial and Textile Employees.
Clark worked his way through Virginia. He told reporters that - despite his own words to the contrary - Clinton administration officials had never pressured him to end the Kosovo war in the summer of 1999 to avoid harming Al Gore's presidential campaign.
The Washington Post, in a report that relied on documents from Clark's tenure as NATO commander, quoted the former general as saying that White House officials had told him to wrap up the bombing by the July 4th weekend.
Clark did not allege being misquoted in the story, but said he had given a military historian a "stream of conscious dictation."