Among white, working-class voters  most commonly identified as those without a college degree  Mrs. Clinton has won by 2 to 1 or better in states like Indiana, Kentucky, Ohio and Pennsylvania. Mr. Obama has fared better among less culturally conservative working-class whites in states like Oregon, where the environment is a central issue for voters. Still, Mrs. Clinton’s claim that she is best positioned to win the “hard-working Americans, white Americans” has become the linchpin of her argument that she is more electable than Mr. Obama.

But Mr. Teixeira, who is not backing either candidate, does not buy that argument. He dismisses intraparty contests as “pretty poor evidence” of whether Mr. Obama, as the Democratic nominee, could attract the blue-collar support he would need against Senator John McCain, the presumed Republican nominee.

No Majority Needed

And how much blue-collar support would Mr. Obama need? Not a majority, said Mr. Teixeira. Though blue-collar Democrats once represented a centerpiece of the New Deal coalition, they have shrunk as a proportion of the information age-economy and as a proportion of the Democratic base.

Al Gore lost working-class white voters by 17 percentage points in 2000, even while winning the national popular vote. Senator John Kerry of Massachusetts lost them by 23 points in 2004, while running within three points of President Bush over all. Mr. Teixeira suggests that Mr. Obama can win the presidency if he comes within 10 to 12 percentage points of Mr. McCain with these voters, as Democratic candidates for the House did in the 2006 midterm election.