Two weeks ago, while most Senate Republicans were focused on the parts of the defense-authorization bill that related to military training and support, several prominent Democrats drafted an amendment to the bill that would have mandated sending terrorist detainees at Guantanamo Bay to the states. The bill never got a vote, but a Republican alternative prohibiting such a move overwhelmingly pass the Senate the following week. Amazingly, every Democrat sponsor of the original amendment ended up voting for the Republican alternative.

The fact that prominent Democrats would so quickly and radically change their minds on a clear-cut issue like this says a lot about the effect that presidential primary politics has on Senate Democrats these days. It’s no coincidence that we’ve spent nearly the entire year on Iraq votes and political investigations of the White House. But the Gitmo vote may be the clearest proof yet that, in key areas, the Democratic agenda is so far out of the mainstream that votes to advance it are hard to defend with the lights on.