Arlen Specter, the bristly former Republican senator from Pennsylvania who often made headlines by playing the political center and confounding Republican colleagues in the Senate, died today at age 82. According to Specter's family, his death was due to complications from non-Hodgkin's lymphoma.

Specter made headlines in 2009 when he announced he was switching his party affiliation from Republican to Democrat. Specter then lost to Joe Sestak in the Pennsylvania Democratic primary and left office in 2011. Sestak lost the general election in Pennsylvania to Republican Pat Toomey.

Specter was also known for originating the "single-bullet" theory  while serving on the Warren Commission, which investigated the assassination of President John F. Kennedy. The theory, accepted by the government as the official explanation for the assassination, held that one bullet, fired by Lee Harvey Oswald, killed Kennedy and then injured Texas Governor John B. Connally.

Specter started his career as a lawyer and then served as Philadelphia District Attorney. In the Senate, Specter made headlines by taking on Republican colleagues for opposing the Supreme Court's Roe v. Wade decision and objecting to the impeachment of President Bill Clinton.

In a statement today, President Obama praised Specter's tenacity in the Senate. "From his days stamping out corruption as a prosecutor in Philadelphia to his three decades of service in the Senate, Arlen was fiercely independent – never putting party or ideology ahead of the people he was chosen to serve," President Obama said.

Senator John McCain (R-AZ), who served alongside Specter in the Senate for 27 years, tweeted: "Arlen Specter - a dear friend who served his state and nation with honor and distinction. RIP."

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