Democratic Candidates Moving Left

But some observers say that the candidates' zeal to appeal to the party's liberal base could cost them in the general election with the independent-minded voters they'll need to win.

That is a particular concern for Democrats if Republicans nominate a candidate who could claim the vast middle of the electorate -- a social moderate such as former New York City Mayor Rudy Giuliani, or a candidate with a long history of reaching out to independents such as Arizona Sen. John McCain.

"Lots of people say, 'I want a Democrat,' but when they see the particulars, they say, 'I don't want that Democrat,'" said Jeffrey Berry, a political science professor at Tufts University. "The thing that's amazing about the Democrats is that they could still snatch defeat out of the jaws of victory. The major Democrats are all now well to the left of the median voter."

Sen. Joseph Biden, D-Del., touched on this concern Sunday on ABC's "This Week." He is the only Democratic presidential candidate to have voted in favor of continuing funding for the war last month.

Biden: American Public Looking for Someone Who Can Win

"Even though the front-runners are good people and they're making a lot of news, they're still getting beaten by the Republicans [in polls], who are generically not preferred by the American public," Biden said. "They're going to be looking for someone who can win."

It's not just the war that shows the leftward tilt of the presidential field. Several Democrats are now talking about raising taxes to expand health insurance to more Americans, or to combat global warming.

All of the Democratic candidates want to reverse the ban on gays and lesbians serving openly in the military, a position that puts them at odds with all of the Republican candidates. The Democrats also want to overturn the federal Defense of Marriage Act, even though it was signed into law by Democratic President Bill Clinton in 1996.

Shift on Health Care Also Striking

An equally dramatic migration has come on health care. In 2004 Kerry offered a plan that would guarantee health coverage to all children; now, the Democrats are arguing over how best to bring universal coverage to children and adults.