Ross explains what he thinks is the risk of Obama:
[Obama] has the potential to do for the Democratic Party what Reagan did for the GOP in '80 - to win a lopsided victory in which a slew of previously-wavering independents and politically-unformed twentysomethings end up branding themselves as Democrats for a generation. That's the good news; the bad news is that if he doesn't win a lopsided victory among independents and young voters - if the bloom comes off the rose or the glass jaw starts to crack - he has the potential to hemorrhage votes in key constituencies: among downscale voters; among seniors (where I suspect the "wouldn't vote for an African-American" constituency is concentrated); among hawkish and extremely pro-Israel Dems; and even among white women. Which is to say, he could win in a walk, or lose thanks to heavy defections from groups that would have trended Democratic had Hillary been the nominee.
My own view, for what it's worth, is that the more Obama campaigns, the more he seems to dispel these reservoirs of doubt. And I think the over-arching argument for an Obama presidency swamps these micro-issues. This is not a Mark Penn election.