The replacement of David Souter counts as a noteworthy issue where Arlen Specter’s decision to switch parties really will make a difference. Over the course of his career, Specter has shown a total lack of principles on judicial nominations. He was an important part of the campaign to spike the nomination of Robert Bork back in the 1980s. But he was the key persecutor of Anita Hill during the Clarence Thomas nominations. During the Clinton years, he hewed a moderate line, then during the Bush years he gave key moderate cover to hard-right nominees.
If we were talking about Arlen Specter, guy who’s trying to fend off a primary challenge from Pat Toomey, you could be sure that he’d vociferously oppose anyone Barack Obama nominated. But as Arlen Specter, guy who’s hoping to avoid a tough primary challenge from the left, he ought to be easy to count on as a supporter. The overall impact of the Specter flip should be pretty modest but I bet this is one of the times it will flip a vote and that, in turn, will help flip the narrative around the whole thing.