Pennsylvania Sen. Arlen Specter is proving to be a loyal Democrat.

Arlen Specter announcing in April he would run in 2010 as a Democrat. (Scott Ferrell/CQ)

Specter, who faces a serious challenge in a 2010 Democratic primary, has demonstrated a higher level of party unity during his brief time as a Democrat than he did as a Republican.

CQ data show that Specter, since bolting the Republican Party at the end of April, has sided with Democrats on 17 of 20 votes that have pitted most Democrats against most Republicans. CQ refers to these party-line or near-party-line votes as “party unity” votes.  

It’s an admittedly small sample — the Senate voted just 51 times between April 30, when Specter’s party switch became official on the voting rolls, and the July Fourth recess, and just 21 of those votes were party unity votes. But Specter’s 85 percent party unity score post-switch demonstrates a large degree of party allegiance for the senator.