Arlen Specter
Sen. Arlen Specter speaks to reporters in November 1995, days before he abandoned a bid for the presidency and endorsed Republican Sen. Bob Dole. (John S. Zeedick / Associated Press)
Sen. Arlen Specter, left, confers with Senate Judiciary Committee Chairman Patrick Leahy (D-Vt.) in 2002 at a hearing about government surveillance powers. (Joe Marquette / Associated Press)
Specter and his wife, Joan, greet supporters after 2004 primary elections. Specter defeated challenger Pat Toomey, a conservative. Toomey is expected to challenge Specter again next November, when the former Republican runs for reelection as a Democrat. (George Widman / Associated Press)
As Senate Judiciary Committee Chairman, Specter, center, listens to testimony on detainee and enemy combatant legal rights in July 2006. He’s flanked by Sens. Orrin Hatch (R-Utah) and Patrick Leahy. (Dennis Cook / Associated Press)
Specter talks to reporters before voting on the economic stimulus bill in February 2009. He was one of three Republican senators to cross party lines and support the $787-billion package -- the three votes were just enough to ensure that the GOP could not block the bill with a filibuster. (Chip Somodevilla / Getty Images)
Vice President Joe Biden talks with Specter. (Saul Loeb / AFP/Getty Images)
Pennsylvania lawmakers surround Specter at a University of Pennsylvania reception to honor his vote supporting the economic stimulus package. (Matt Rourke / Associated Press)
Then-Sen. Arlen Specter in his office in 2009. (Nancy Stone / Chicago Tribune)
Specter speaks at a Senate Appropriations Committee emergency hearing about swine flu on Tuesday, the day he announced he was leaving the Republican Party. (Tim Sloan / AFP/Getty Images)
Sen. Tom Harkin (D-Iowa) greets Specter. Specter ran for reelection to the Senate as a Democrat in 2010. I have found myself increasingly at odds with the Republican philosophy and more in line with the philosophy of the Democratic Party, he said. (Michael Reynolds / EPA)