With much of the establishment backing Lieberman, Lamont initially built his campaign with the support of grass-roots activists disaffected with the incumbent and the president. Liberal bloggers around the country promoted his candidacy, helping to raise his profile, attack Lieberman and attract money (although Lamont's personal fortune has financed most of his campaign). They helped give voice to rank-and-file Democrats furious with Bush and frustrated by what they regard as cautious and ineffective party leadership in Washington and to some local elected officials angry with Lieberman.

Lieberman enjoys the support of the party's national leadership, along with most of organized labor and key constituency groups. Former President Clinton came here two weeks ago to campaign for Lieberman. Hillary Clinton has said she wants Lieberman to win. Senate Democratic leaders back his candidacy and months ago urged MoveOn officials to stay out of the primary.

If Lamont wins the primary, they will be forced to shift allegiance. Both Clintons have said they will support the winner of the primary and other party officials plan to do the same.

Lieberman, however, has said that, if he loses, he intends to run as an independent in the general election. Party officials will have to decide whether to press him to abandon those plans and, if he declines, how strongly they get behind Lamont's candidacy. Democrats hope to pick up three vulnerable Republican-held House seats in November and do not want a distracting Lieberman-Lamont general election battle to get in the way.

Rep. Rahm Emanuel, D-Ill., chairman of the Democratic Congressional Campaign Committee, said Friday he is not worried about the fallout from the Senate primary on House races, arguing that the message from Connecticut is that anyone supporting Bush's war policies is in deep trouble. "What's playing out here is that being a rubber stamp for George Bush is politically dangerous to life threatening," he said.

Republican pollster Bill McInturff sees the Connecticut Senate race as a critically important event in shaping the midterm campaigns. "This will embolden Democrats around the country," he said. "I think that this primary in its own way sets off a chain of events that makes the fall elections very quickly a debate that could be framed as a (Democratic) timeline (for withdrawing U.S. forces) versus Republicans supporting a longer term solution."

All of that may bode well for the Democrats, given sentiment about the war. As Democratic pollster Peter Hart put it: "What (Connecticut) tells us about the fall is something I think we've known all along and that is the status quo in Iraq is unacceptable. It's unacceptable to Democratic primary voters, it's unacceptable to independents and it's unacceptable to a large minority of Republicans."

Connecticut is a liberal, Democratic-leaning state, by no means a reflection of the rest of the country, which is one reason some strategists caution against reading too much into results here.

Borosage, who has battled moderates in the party for years, offered a word of caution for Democrats. Without a muscular alternative to Bush's policies, he said, "I think the debate this fall is going to be a difficult debate, even with the war unpopular."