Senate Democrats and Senate Republicans have almost perfectly analogous situations in Kentucky and Connecticut. Each is a totally safe state, but facing a high danger of electing a Senator of the opposite party in 2010 because of a wildly unpopular incumbent: Republican Jim Bunning in deep-red Kentucky, and Democrat Chris Dodd in deep-blue Connecticut. The parties have a strong incentive to force their incumbents to retire, but the incumbents themselves obviously have no reason to quit. So the contrast is an interesting experiment in which party has more influence over its members.
Now Politico reports that Bunning is poised to retire, which will make the Kentucky seat extremely safe. Can Democrats pull the same trick in Connecticut? We'll see.