"I have taken a pretty good bunch of hits from all of the opponents and all of you guys," the former Vermont governor said after he was beaten into third place by senators John Kerry and John Edwards in the Iowa caucuses.
"We were pretty much the target of everybody for a long time. And it's hard to sustain that," he told CNN television.
Dean said the defeat would not derail his campaign for the White House, and that he would campaign harder than ever starting with the primary election in New Hampshire on 27 January - the next state on the nomination list.
"Not only are we going to New Hampshire ... we're going to South Carolina and Oklahoma and Arizona and North Dakota and New Mexico," Dean shouted at his stunned supporters.
"And then we go to Washington DC to take back the White House!" he shouted.
"We will not give up. We will not quit now or ever. We want our country back for ordinary Americans."
Dean had been an outsider when he launched his campaign, but forced his way to the front using the internet to sign up tens of thousands of supporters and collected 40 million dollars in donations last year alone. He had also led opposition to the US invasion of Iraq.
Dean insisted his result had still been an achievement. "If you had told us one year ago that we were going to come in third in Iowa, we would have given anything for that," Dean said to roars of approval from a crowd of flag-waving supporters.
Dean (L) insists Democrats have
to include every faction to win
He warned rivals that the Democratic Party could not win the presidency unless it included every faction, including his.
"We are an outsider campaign, we're an insurgent campaign," he declared.
"The truth is the other Democrats can't win and beat George Bush without the people we are bringing to the party. We can't win without the people they are bringing to the party. And that's the process I started."
While some have hailed Dean as a breath of fresh air for the Democratic Party, some party leaders have expressed concern at his short temper which has gained him a reputation as a loose cannon.
Dean ran a populist campaign, slamming the Washington elite and vowing to reach out to blacks, Hispanics and working class whites - key sectors for any Democrat seeking to lock up the party's nomination.
Dean ran a populist campaign, slamming the Washington elite and vowing to reach out to blacks, Hispanics and working class whites
He locked up several key union endorsements last year and garnered endorsements, including from former vice president Al Gore - the Democratic contender in the 2000 presidential race - former US senator Bill Bradley, and Iowa's Democratic Senator Tom Harkin.
The untested coalition of young voters who helped propel Dean to frontrunner status in the Democratic presidential race failed to help him at the Iowa caucuses.
The vote in Iowa was a setback not only for the Vermont governor, but for the youthful "Generation Dean" supporters who helped him break fundraising records and had pushed him to the top of the polls.
Dean says a quarter of his
supporters are younger than 30
Dean has said a quarter of his contributors are people younger than 30, who in many instances are estranged from politics but can in the near future become core Democrats.
"That's how you rebuild our party," he has said on the campaign trail.
"Deaniacs" - first-time political evangelists armed with cell phones, voter lists and political leaflets - were expected to be a formidable organising force in this state.
But in the end their energy and enthusiasm had failed to dispel voter doubts about Dean's electability and concerns about his viability as an alternative to the Republican president.