Arlen Specter, the former senator from Pennsylvania who stunned both parties on Capitol Hill in 2009 when he announced he would switch his party allegiance to Democrat after 42 years as a Republican, has died. He was 82.
Specter died at his Philadelphia home from complications of non-Hodgkin's lymphoma.
Specter's battle with cancer has been long. In addition to the removal of a brain tumor, he was diagnosed and underwent chemotherapy for Hodgkin's disease in 2005, only to undergo treatment again when it resurfaced in 2008.
He published a book, "Never Give In: Battling Cancer in the Senate," about dealing with the disease after his initial diagnosis.
President Obama said Specter was "always a fighter."
"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. He brought that same toughness and determination to his personal struggles, using his own story to inspire others," Obama said in a statement.
In August, Specter announced he was "battling cancer" again -- this time with non-Hodgkin's lymphoma.
"I'm battling cancer. It's another battle I intend to win. I'm grateful for all the well wishes I've received. I'm looking forward to getting back to work, to the comedy stage, to the squash court and to the ballpark," Specter said in a statement released through his Philadelphia office, The Associated Press reported.
Last month, he was released from a Philadelphia hospital.
He is survived by his wife, Joan, and two sons, Shanin and Stephen.
Born in Witchita, Kansas, in 1930, Specter was the youngest son of Lillie and Harry Specter, a Ukrainian immigrant. While in college, Specter said the Jewish family uprooted from Kansas and moved to Philadelphia when his sister came of age so she could find eligible bachelors of their faith.
After serving stateside with the Air Force during the Korean War, Specter returned to college to pursue a law degree at Yale.
He was admitted to the Pennsylvania bar in 1956 and served as assistant district attorney of Philadelphia from 1959 to 1964.
Specter began his political career when he was appointed assistant counsel to the Warren Commission, the congressional body tasked with investigating the assassination of President John F. Kennedy. Recruited at the recommendation of then-Rep. Gerald Ford, Specter became one of the original proponents of the "single bullet" theory.
Specter wrote about that experience in his book, "Passion for Truth: From Finding JFK's Single Bullet to Questioning Anita Hill to Impeaching Clinton," which was published in 2000.
In 1965, Specter was elected district attorney of Philadelphia, where he served two terms until his defeat in 1973. After failed bids for congress and the Pennsylvania governor's office, he eventually was elected to the Senate in 1981.
Specter's Political Career
In his three decades -- five terms -- in the Senate, Specter was a formidable presence on Capitol Hill, chairing three committees during his Senate career: the Intelligence, Judiciary, and Veterans Affairs committees.
Specter participated in 14 Supreme Court confirmation hearings and took leadership roles on legislation including the Armed Career Criminal Act, the Terrorist Prosecution Act, the Hate Crimes Act and legislation to expand Veteran's Rights, legislation to reform asbestos litigation, legislation for education and worker safety and the bill that created the Inspector General of the CIA.
In October 2002, Specter voted for authorizing the Iraq war.
In 2007, Time magazine honored him as one of "America's 10 Best Senators," pointing to his legislative achievements and the help he provided in securing expanded funding for the National Institutes of Health.
A career moderate, as a Republican Specter had a long record of bucking his party even while in leadership positions. He was a sharp critic of President Bill Clinton's healthcare proposals and sought the GOP presidential nomination to run against him in 1996. But two years later he would go on to vote "not proven" during Clinton's impeachment hearings, believing the president had not received due process.
As Judiciary Committee chair in 2006, he called then-Attorney General Alberto Gonzalez to testify on the Bush administration's warrantless wiretapping of U.S. citizens, a practice he openly criticized.
During the scandal the same year around the leaking of CIA operative Valerie Plame's identity, Specter said President Bush, "owes a specific explanation to the American people," over the circumstances, adding that even if "the president may be entirely in the clear, and it may turn out that he had the authority to make the disclosures which were made, it was not the right way to go about it because we ought not to have leaks in government."
Specter's Party Switch From Republican to Democrat
Besides his time spent on Capitol Hill, Specter may be best known for his 2009 party switch, which played a key role in helping President Obama get his flagship legislation though Congress.
Specter called his decision to switch from Republican to Democrat "painful," and said he made the decision based on public and private polling in Pennsylvania that showed "the prospects for winning a Republican primary [in Pennsylvania] are bleak.
"As the Republican party has moved farther and farther to the right, I have found myself increasingly at odds with the Republican philosophy and more in line with the philosophy of the Democratic Party," Specter said at the time..
Senate Republican leaders admitted they were unhappy losing a member, but argued that it had nothing to do with the national Republican Party rejecting moderates, but only with local Pennsylvania politics and Specter's desire for "political self-preservation."
In 2010, Specter lost the Democratic primary to then-U.S. Rep. Joe Sestak, who in turn lost the race to Republican Pat Toomey.
Specter supported the Obama administration's controversial American Recovery and Reinvestment Act -- the stimulus -- and Wall Street reform as efforts to get the economy back on track after the collapse of 2008.
But perhaps most stinging to the Republican party, Specter's vote was the magic number 60th vote, to pass Obama's health care reform legislation in the Senate in December 2009.
In March of this year Specter spoke out about what he saw as the gridlock that has all-but paralyzed Congress this year.
"The cannibals have taken over and it has produced a gridlocked Senate and a dysfunctional government," Specter said in an interview with CBS News. "Like cannibals eating their own, that's what's happening in Washington. ... You had a senator like Bob Bennett, with a 93 percent conservative rating, he cast one vote to support the bailout of the auto industry and he got dumped by the Republican Party."
Senate Majority Leader Harry Reid, D-Nev., released the following statement today on Specter's passing:
"I was deeply saddened today to learn of the passing of Senator Arlen Specter. I served with Senator Specter in Congress for twenty-eight years. Senator Specter was a man of moderation; he was always passionate, but always easy to work with. I followed him through his previous illnesses, during the course of which he displayed great physical strength and great strength of character. Throughout his life, Senator Specter fought and won many battles, but this was one he could not win," Reid said in the statement. "America is better today because of Arlen Specter. He will be dearly missed."
After he left politics, Specter resumed his former career as an attorney, and served at his former alma mater, the University of Pennsylvania, as an adjunct law professor.
He was even seen touring the Philadelphia comedy club circuit, jokingly lamenting over his days on the Hill, Bill Clinton, and former Pennsylvania Gov. Ed Rendell.
ABC News' Zach Wolf and The Associated Press contributed to this report.