How much does party caucusing contrain Senators' votes?

[DSeid]

Of course inspired by Specters leap and by talk about Snowe and Collins … but informed by 538’s take on it.

All of the party-switchers moved toward the direction of their (new) party caucus after making the change, although with somewhat varying degrees of magnitude. California’s Matthew Martinez, for instance, who had not been an exceptionally moderate Democrat, turned all the way into a rather run-of-the-mill Republican. On the other end of the spectrum, you’d have had to look pretty hard to find issues on which Congressman Gene Atkinson of Pennsylvania was voting differently after becoming a Republican in 1981.

The average magnitude of the change was ±.394 points, with about two-thirds of the cases somewhere between ±.3 and ±.5.

What does this mean for Specter? If we take his rating of +.091 from the 110th Congress and subtract .394 points from it, we come up with a -.303. That would make him similar to Tim Johnson (-.282), Blanche Lincoln (-.297), Kent Conrad (.315) or Joe Liberman (-.333). Bob Casey Jr, by contrast, Specter’s colleague from Pennsylvania, rates as a -.401, whereas the average Democratic senator in the 110th Congress was a -.441.

There are both aggravating and mitigating circumstances that may affect Specter’s positioning. On the one hand, he seems to have made the switch more or less unabashedly for electoral reasons, even alluding to the polling in his statement today. This suggests that he’ll be no more and no less Democratic than he can get away with. On the other hand, the parties are now more polarized than they once were, and so crossing the aisle may mean more than it once did. Prior to this party-switch, Specter’s DW-NOMINATE scores had gradually been moving away from the center as it had become harder to stake out a position as a moderate Republican.

So on average a switch does come with some change in voting pattern, but not usually reliability. Specter may have been moving slightly Rightward some just as a pragmatic matter and now may be more free to move back towards to center. Snowe however is already as in the middle as we’ll find and has no reason to feel contrained either way by which letter she has attached. Or does she?

[Lantern]

Off all those cases Jeffords would seem to be the closest. Moderate, NE Republican, senator and relatively recent. His shift is pretty similar to the mean shift anyway so it would seem a good estimate for how much Specter moves.

A lot depends on tactics as well. Specter will be watching out for the Democratic primary and see if he gets challenged from the left. He may move quickly to the left to preempt any challenges. Until he gets the nomination he is quite vulnerable and Obama needs to exploit that to push through his upcoming legislation. Specter won’t be an automatic 60th vote but it will be very awkward for him to be the only dissenting Democrat particularly on major legislation. So if Obama gets the other 59 votes, getting the 60th vote is now substantially easier than earlier.