Washington is all astir today at the bombshell news that Republican Senator Arlen Specter will leave the GOP and join the Democratic Party, bringing Democrats within reach of a filibuster-proof majority—if and when Al Franken is seated as Minnesota's senator. A 29-year senate veteran and the fifth-oldest senator, Specter is switching his party affiliation now so he can run in the Pennsylvania Democratic Senate primary.

Earlier this year Specter was one of three GOP senators to back President Obama's $787 billion economic stimulus plan, a move that was strongly condemned by conservatives but played better in his home state—which has seen some 200,000 Republicans migrate to the Democratic Party, according to a statement he released at noon:

Since my election in 1980, as part of the Reagan Big Tent, the Republican Party has moved far to the right... I now find my political philosophy more in line with Democrats than Republicans. Since then, I have traveled the State, talked to Republican leaders and office-holders and my supporters and I have carefully examined public opinion. It has become clear to me that the stimulus vote caused a schism which makes our differences irreconcilable. On this state of the record, I am unwilling to have my twenty-nine year Senate record judged by the Pennsylvania Republican primary electorate.

Sources tell Politico

that Specter made his decision after seeing a recent poll showing him badly trailing former Congressman Pat Toomey in the Republican primary. After being informed of his decision, President Obama called Specter to say, "You have my full support. [We're] thrilled to have you." The news seems to have caught the GOP by surprise; former Republican Pennsylvania Senator Rick Santorum called it "a huge blow to the Republican's ability to moderate any of Obama's very liberal proposals. I can only hope that Arlen will be as independent as a Democrat as he has been as a Republican.”