Based on his 2001 campaign and record as Governor, Warner's biggest problem will come from the left. The DKos types haven't had opportunity to bash him excessively yet, but once the leading leftists in the 2008 attack Warner, their shills will join.
The DKos types? What is that supposed to mean? Daily Kos is a great site with some real, in-depth political discussion.
I read Daily Kos all the time and the only bad thing I've ever heard about Warner is that he lacks charisma. Besides that, I think most "DKos types" would gladly support him. I know I would.