Make a good VP, that is.
Poltiblog explains why:
Beyond the general difficulties for Obama of dealing with Hillary (as well as Bill), I think that the main chance that the Democrats have of wooing independents and some Republicans is an Obama ticket sans Clinton. While I lack empirical evidence to support the argument at the moment, I think that the general dissatisfaction with the Bush administration, mixed with the unpopularity of the Iraq War will translate into a number of Republicans being willing to vote for Obama in the Fall. However, those same disgruntled Republicans have a great deal of animosity aimed in the direction of the Clintons and will be utterly unwilling to vote for a ticket that contains a Clinton and they will either stick with McCain, cast a protest vote for Barr or stay home in November.
Put another way: an unpopular war and economic problems equals problems for the incumbent party–in a generic sense there is plenty of historic evidence to support such an assertion. Under such conditions, voters normally predisposed to vote for that party will defect or abstain. As such, it is reasonable to assume that Obama has a real chance of winning a decent number of Republican votes in the fall. However, Republicans, in general, have a great deal of dislike for the Clintons, and her presence on the ballot would suppress, to a substantial degree I believe, the generic pattern described in the first portion of this paragraph. As such, Obama-Clinton is far less of a “dream” for the Democrats as many pundits may think.