With at least 2,500 supporters crammed into a brick-lined town square, the steeple of a Unitarian church behind him, the former Vermont governor pledged to speak "for a new American century and a new generation of Americans."
Dean pledged to fight conservative Republicans, docile Democrats and the rest of the Washington establishment — all of whom he holds responsible for turning Americans away from the political system.
"You have the power to take our country back!" he shouted. "You have the power! You have the power! You have the power!"
He accused Bush of dividing Americans, creating a "chain of insurmountable debt" and promoting tax cuts "designed to destroy Social Security, Medicare, our public schools and our public services through starvation and privatization."
The president's foreign policies, Dean argued, have alienated allies much like the ancient Roman empire once did. "Every American president must and will take up arms in the defense of our nation. It is a solemn oath that cannot and will not be compromised," said Dean, knowing he faces questions about his lack of foreign policy experience.
"But there is a fundamental difference between the defense of our nation and the doctrine of pre-emptive war espoused by this administration," Dean said. "The president's group of narrow-minded ideological advisers are undermining our nation's greatness in the world."
Dean, 54, a 20-year veteran of Vermont politics, actually began his campaign months ago. But he staged a formal announcement to draw attention and money to his long-shot bid.
The nine Democratic candidates are in a race for cash before the second fund-raising quarter closes June 30. Dean is expected to raise at least $4 million by the deadline, a jump from the $2.6 million he collected in the first quarter, a senior campaign official said.
Dean is airing the first political ads of the 2004 campaign, spending $300,000 in Iowa through July 2. Supporters were urged through e-mail last week to help pay for the TV time.
Besides a crowd here that spilled from an intersection into two nearby streets, 15,000 Dean supporters had signed up to attend campaign events in more than 300 cities.
A turnout of that size would validate Dean's boast that he is building an Internet-driven, national grass-roots organization. It was impossible to verify Dean's projections, but in one city, Des Moines, Iowa, 87 supporters signed up to watch his address at the campaign headquarters; 47 showed up.
"It's a good way to get out of the office," said Ben Stone of Des Moines.
A former governor in a race dominated by congressional Democrats, Dean has gotten off to a surprisingly strong start despite a lack of money and meager support from party insiders.
The key has been his opposition to the U.S.-led war against Iraq
a position that galvanized liberal voters who believe that Democratic leaders are kowtowing to Bush.
In a call to disenchanted voters of all political stripes, Dean said, "You have the power to rid Washington of all the politics of money."
"You have the power to take back the Democratic Party."
The liberal tag defies his record in Vermont, where Dean was known as a centrist, pro-business governor for 12 years.
He battled Democrats to restrain spending and balance the state budget, even pushing for cuts in human services programs such as benefits for the aged, blind and disabled.
He nominated tough-on-crime judges, most of them former prosecutors. And he imposed work requirements on welfare recipients well before former President Bill Clinton did.
As governor, some of his strongest supporters were Republican leaders of the business community. Difficult to label, Dean once called himself "an odd kind of Democrat."
Now that he's a presidential candidate, Dean is not trumpeting his moderate credentials from Vermont, nor did he dwell on his anti-war position during Monday's address.
Instead, he sought to widen his appeal by casting himself as a blunt-speaking, anti-establishment populist who will reform American politics issue by issue.
"This president has forgotten ordinary people," Dean said.
The physician-turned-politican once intended to make health care and children's issues the cornerstones of his campaign, but then came the war and his introduction to a disenchanted electorate. His cause changed, Dean said.
"Everywhere I go people are asking fundamental questions: Who can we trust?" he said.
Dean hopes to galvanize Democrats who have not voted in recent elections, as well as independents who rallied behind insurgent candidates such as Republican Sen. John McCain in 2000 and Democrat Gary Hart in 1984.
Polls place Dean among the top three candidates in Iowa and New Hampshire, where the first votes for the Democratic nomination will be cast. He lags in nationwide polls.