In VA, it's certainly possible. Warner v. Kilgore would be a tough race.
to Scoonie, jfern, other crazy leftists: Warner is just fine by the Kossacks and their ilk only because he's a Governor, and most of their criticism is aimed at Capitol Hill. Few really know his record or followed his 2001 campaign. Most of all, Warner is not in a primary yet.
Were Warner to enter the primary, people would start picking sides, and it would be a race to the left. A race Warner can't win, and for that he would be abandoned by Democratic activists. This is fairly obvious game theory and if Warner enters the race that's exactly what will happen.
The only X factor is if the Democrats are destroyed in 2006.
Did you read the speech? He could easily win the primary. It's not just about exactly where they are on the political spectrum, it's also about how they can frame their message and stand up to the Republicans. He looks pretty damn good.
As for 2006, anyone who is predicting more than 4 seat change either way in the Senate is crazy.