"We're going to fight for the heart and soul of the Democratic Party," Lamont told more than 100 supporters at the Old State House. "With your passion, your enthusiasm, the grass roots, the Net roots - we're going to show people on a hot day in August that we can win. We can win not by being Republican Lite, but by being proud Democrats."
Lieberman's campaign monitored the announcement and quickly accused Lamont of negative campaigning, signaling that the senator views Lamont as a serious threat in a Democratic primary, where the voters tend to be liberal.
Tom Swan, Lamont's campaign manager, said Lamont attacked Lieberman's record, not his integrity.
"That's what their focus groups tell them they have do, portray Ned as angry. That's asinine," Swan said. "We're going to talk about Lieberman's record. It would be a good record - for a Republican from Mississippi."
The Democratic establishment is with Lieberman.
"They tell me, `Ned, don't rock the boat,'" Lamont said in a quavering voice, mocking party leaders. "Baby, I say it's high time we rock the boat."
Lamont intends to campaign on the full range of progressive Democratic issues, including universal health care and abortion rights, but his comments on the war generated the most enthusiastic applause Monday.
Bush and Lieberman have dragged the U.S. into a civil war that has made the world a more dangerous place, he said.
"They said the war would be easy. They said we would be greeted as liberators. And here we are three years later, America is no safer. Israel is no safer. The Middle East is destabilized. Iran is on the prowl. Osama Bin Laden is still on the prowl. We have 135,000 troops stuck in the middle of a bloody civil war," he said. "And I say that those who got us into this mess should be held accountable."