By joining the Democratic Party, Specter is in some ways returning to his roots. In 1965, when he ran for Philadelphia district attorney, he thought he'd do it as a Democrat—but the party machine didn't want him, so he ran on the other ticket. * Since then, he has governed in the mode of Hugh Scott, the longtime moderate from the same state. Specter has long been considered by die-hard Republicans a RINO (Republican in Name Only). In 1996, he ran for president on a pro-choice platform, which didn't get him very far. This year, he was one of three GOP senators to back Obama's $787 billion economic stimulus plan.
Former U.S. Rep. Pat Toomey, who ran against Specter once before and almost beat him, used that vote as the launching pad for his candidacy. The Republican Party has lost a lot of voters over the last years, and polling showed Toomey up by 10 points in a GOP primary. Specter was considered a political dead man walking. There's not yet any reliable polling with Specter as a Democrat, but at least now the two-time cancer survivor has a fighting chance to reach the general election.
Update, 7:09 p.m.: Before Specter was a Democrat, Joe Torsella (now his Democratic primary opponent) called him to let him know that he was getting into the race. This morning Specter returned the favor, calling Torsella to let him know that he was switching parties and that he would now be Torsella's opponent sooner than anyone thought. Specter's opponent was apparently so surprised, he had very little else to say other than to thank Specter for the courtesy. A source close to the campaign reaffirms that even though Obama and Gov. Rendell are likely to work for Specter, Torsella is staying in the race. A source familiar with Democratic senatorial campaigns reminds that such a stalwart posture can mean Torsella really isn't going anywhere—but it might also mean that he's negotiating for something in exchange for being a good Democrat and clearing the way for Specter.
Correction, April 28, 2009: This article mistakenly said Specter ran for Pennsylvania state attorney general in 1965. ( Return to the corrected sentence.)