Senator Arlen Specter has changed his party affiliation today, leaving the Republican party that he has caucused with as senator since 1981 to join the Democratic party.

Spector has been accused of having liberal voting tendencies by the more conservative wing of the Republican party and he would have faced a primary challenge in 2010. Presumably he sees an easier path running in Pennsylvania as the Democratic candidate.

Nate Silver, of 538, says this is more of a blow to the Republican Party than a boon for the Democrats due to the fact that Specter’s vote will probably not change. He was already sometimes voting with the Democratic party, and will more than likely be one of the more moderate, right leaning Democratic senators. Then again Silver goes on to point out that Specter will have to be careful in his new party as well, since Democrats could find it just as palatable as Republicans did to challenge him in a primary.