I think it's a safe assumption that the reason that the incumbants who ran for a second term and won while in war time is that war unites the country. I am betting that this will not be the case this time. One of Bush's primary slogans was that he was going to be a uniter, not a divider. The Iraq war is about as divisive a war that there could be.

Kerry will have to demonstrate that he is a uniter, not just a partisan who is critical of the Bush administration.

The selection of the Vice President may help Kerry's ability to unite. However, I think the VP of a Kerry Administration will not have near the impact that Cheney has on the Bush Admin.