Is Barack Obama doomed in a matchup with John McCain among the demographic groups where he did poorly against Hillary Clinton? The AP says not really:
Polls this month show the Illinois senator leading McCain among women, running even with him among Catholics and suburbanites and trailing him with people over age 65. Results vary by poll for those without college degrees. And though Obama trails decisively with a group that has shunned him against Clinton -- whites who have not completed college -- he's doing about the same with them as the past two Democratic presidential candidates.
The key fact here is "doing about the same" with whites who lack a college degree as Al Gore and John Kerry. Gore and Kerry both lost narrowly, but they lost. On the other hand, though they both lost, they lost narrowly. I think it's totally feasible to win the presidency without improving on the Gore/Kerry performance among this demographic group (you'd have to make up the ground elsewhere), but it's hard for me to see how it would be viable to slip further behind and still win.