HARRISBURG, Pa. — Arlen Specter, who spent much of his pugnacious 30-year career in the U.S. Senate warning of the dangers of political intolerance, lost a battle with non-Hodgkin lymphoma at a time when Congress is more politically polarized than anyone serving there — or living in America — can remember.

Specter, who died Sunday, is remembered as one of Congress’ best-known moderates.

He was a member of both major parties during his career and even mounted a short-lived run for president in 1995 on a platform that warned his fellow Republicans of the “intolerant right.”

Now, two years after he was voted out of office, his death coincides with a finding by political scientists that Congress is more polarized than at any point since Reconstruction.

Specter lost his job amid the very polarization that he had repeatedly attacked: He crossed political party lines to make the toughest vote he had ever cast in his career when, in 2009, he became one of three Republicans to vote for President Barack Obama’s economic stimulus bill.

Republican fury drove Specter to the Democratic Party, where he lost the 2010 primary.

“When he cast a vote on the stimulus, I think he knew he had no future in the Republican Party,” said Ed Rendell, a former Pennsylvania governor who began his career in public service as a deputy district attorney under Specter in Philadelphia.

Former Pennsylvania Gov. Tom Ridge, who served six terms in the U.S. House and as President George W. Bush’s first Homeland Security secretary, said he thinks a serious third party could emerge on the national stage in 2016 without bipartisan agreement on major issues including the debt and immigration.

“I think the American public is fed up with the inability of both parties to find common ground,” Ridge said Sunday.

Sen. Bob Casey, D-Pa., who served four years with Specter and is seeking re-election as a moderate, said Sunday that he believes moderates can still bring people together.

“It’s not going to happen naturally or by accident,” Casey said. “Each individual member of Congress has to take on personal responsibility. ... He has to keep the poison out of the water to avoid the kind of demonization that happens when people debate issues.”

Specter, Casey said, was one of those people who could disagree without demonizing.

The other two Republicans who supported Obama’s stimulus are Maine’s two U.S. senators. One of them, Olympia Snowe, announced in February that she wasn’t seeking re-election. She said she was frustrated by “‘my way or the highway’ ideologies.”

In one study of congressional polarization, University of Georgia professor of political science Keith Poole mapped the political polarization of Congress by charting votes and found that the parties are more divided than at any time since Reconstruction after drifting further apart in the last 40 years.

Poole said in an essay that there are no true moderates left in the House of Representatives, and just a handful remaining in the Senate, in contrast to the Reagan era when about half of the members of Congress could be described as moderates.

For Specter, the benefit of crossing party lines wasn’t always about being true to his convictions. He also used it to benefit the causes he championed.

“He was a master politician,” Rendell said. “He was as smart as a whip.”

In his 2004 run for re-election, Specter was endorsed by both the AFL-CIO of Pennsylvania and the arch-conservative Rick Santorum, then Pennsylvania’s junior senator. Santorum later said Specter had pledged to support then-President George W. Bush’s nominees to the Supreme Court, regardless of their views on abortion rights. Specter, who supported abortion rights, had said he never would make such a promise under any circumstance.

In 2001, he voted for Bush’s package of tax cuts, but voted with Democrats to route $450 billion into education and debt reduction. He negotiated $10 billion for medical research when he agreed to vote for the stimulus.

Specter, who grew up in Depression-era Kansas, justified his vote for the stimulus as the only way to keep America from sliding into another depression.

But Specter had barely won his 2004 Republican primary and decided that the stimulus vote had ensured his political career would not survive another GOP primary. At the urging of good friends Vice President Joe Biden and Rendell, both Democrats, he switched parties.

Still, many Democratic primary voters had never voted for Specter, and they weren’t about to start.