The Connecticut race may be seen as an intensification of the partisan, polarized politics of the Bush era. Lieberman is paying a price for being an advocate of bipartisanship.

As a result, a loss Tuesday could generate more demand for a strongly anti-Bush, antiwar candidate in the Democratic primaries. Several are ready to run, including Sen. John Kerry (Mass.), former senator John Edward (N.C.) and Sen. Russell Feingold (Wis.), the only one of the three to vote against the war in 2002.

None, however, may be as attractive to the grass-roots activists as Gore. He has said he cannot conceive of circumstances that would put him in the race but may be coaxed to reconsider.

Republicans already are seeking to exploit a possible Lamont victory as a sign that Democrats are moving too far to the left on national security issues. "They want retreat — under the guise of 'reducing the U.S. footprint in Iraq,' " William Kristol writes in the latest issue of the Weekly Standard.

Sen. Christopher Dodd, D-Conn., said it is a mistake to claim, as the Republicans are doing, that the Democrats have been captured by left-wing, antiwar activists, saying. "This is really about Bush. ... It's deeper than an anti-war thing."

Still, many Democratic moderates say they see worrisome parallels to what happened to the Democrats during Vietnam, when they opposed an unpopular war but paid a price politically for years after because of a perception the party was too dovish on national security. "Candidates know they cannot appease (antiwar) activists if they are going to run winning national campaigns," said Will Marshall, president of the centrist Progressive Policy Institute. "It will intensify the tension inside the Democratic coalition as we head into two critical elections."

But leaders of the so-called netroots activists, and some party strategists, argue that Democrats stand to gain politically by aggressively challenging Bush's war policies. Parallels to Vietnam are inaccurate, they say, because of the nature of an Iraq war that now has become a low-level sectarian civil war.

"If Democrats were winning elections, that prescription would be something worth listening to," said Tom Mattzie, Washington director of MoveOn.org, said in response to the party's moderate wing. "That's the prescription people have been giving us and we've been losing elections."