The likely Rand Paul victory in the Kentucky Republican primary today should give Democrats a very good chance of winning in the fall because supporters of Trey Grayson, Paul's main opponent, really don't like him.
Some primaries play out in such a way that party loyalists view several of the candidates favorably and just choose the one they like best. That was very much the case with the recent Democratic contest in North Carolina. But in Kentucky we find that Paul's supporters hate Grayson, and that even more Grayson's supporters hate Paul.
53% of likely Grayson voters for today have an unfavorable opinion of Paul to only 23% with a positive opinion of him. More importantly though just 40% of Grayson voters say they'll support Paul in the general election if he wins the Republican nomination with 43% explicitly saying they will not.
Paul is going to have some serious work to do to unify his party around him, especially because his supporters have gone out of their way to poke Grayson (and by extension his voters) in the eye. Whether the Democratic nominee is Dan Mongiardo or Jack Conway there's going to be an opportunity to pick up the Republican voters necessary to pull an upset this fall. Democrats winning in Kentucky in a tough political climate for the party is not something you would expect- but neither is Republicans winning in Massachusetts in any political climate. 2010 is really shaping up as the year of the unexpected in politics.