Sen. Arlen Specter [R, PA] is one of the Republicans most likely to vote with Democrats and help them overcome Republican filibusters on key votes. According to our voting trend analysis (scroll down half page here), he votes with his party, the Republicans, only 48 percent of the time. Not surprisingly, he is facing a very difficult primary race in 2010.

Alexander Bolton for The Hill writes that Specter’s best chance for remaining a U.S. senator after this session likely involves switching parties and running as a Democrat:

Sen. Arlen Specter (R-Pa.) does not have the fall-back option of running as an independent should he lose his 2010 primary election, giving the senior lawmaker strong incentive to abandon his party this year.

Specter faces an extremely difficult primary race against former Rep. Pat Toomey (R-Pa.), the conservative firebrand who lost his bid to oust Specter from his seat in the 2004 GOP primary by a mere 17,000 votes (out of more than a million cast).

Pennsylvania political experts say that Specter would likely face a more difficult challenge in 2010 because the Republican primary electorate in Pennsylvania has become more conservative.

“I think he has a lot of problems,” said Terry Madonna, a professor of political science at Franklin and Marshall College in Lancaster, Pa. “I think this is the test of lifetime.”

Madonna estimated that between 150,000 to 200,000 centrist Republicans switched registration to the Democratic Party in the 2008 election cycle, leaving the remaining GOP electorate more conservative.

If he makes the decision to switch, he’ll probably become an even more reliable cross-over for the Democrats and help them pass key bill coming up this year, including card check, health care reform, climate change legislation, and banking regulations.

Some of the key votes that Specter has voted with the Democrats on so far this year include D.C. voting rights, the stimulus bill, S-CHIP and the Lilly Ledbetter Fair Pay Act.

View Specter’s full voting history, including information on which votes were with his party and which were against his party, and use our head-to-head vote comparison tool to see how he compares to other senators from both parties.

Article Tags: Senate Specter