Polls are indicating that either one of the Republican challengers could defeat him in 2010.
There are two ways to approach this news: 1) Harry Reid finds some spine and therefore some much needed support from the netroots, or 2) If it looks unlikely he'll survive, why not recruit a strong primary challenger who could stand an equal or better chance of winning?
Of course I support #2. In fact, I would almost accept a Republican taking Reid's seat if it meant getting a different majority leader. One with some spine/nards.