For 30 years, Arlen Specter stood as a symbol for so much that now seems to have disappeared from today’s Senate.

Specter, the five-term ex-senator who died Sunday, occupied a space in the Senate that no longer fits the current political environment: raging centrist. From the day he was first sworn in in January 1981, Specter spent his career finding ways to enrage both ends of the ideological spectrum, throwing his always sharp elbows at liberals one month only to do the same to conservatives the next month.

In the last hour before voters sent him packing, Specter invoked a favorite cartoon fighter to sum up why he never changed his style — even as he twice changed his party affiliation.

“Remember Popeye, who used to say, ‘I am what I am’? I don’t think anyone could dress me in different attire. I am what I am,” Specter told reporters just minutes before polls closed in the May 2010 Democratic primary.

Specter lost that day to a two-term liberal congressman who would lose in the general election, ending the career of Pennsylvania’s longest-serving U.S. senator. Specter’s defeat, and now his death 21 months after leaving office, signaled the demise of the tough-minded centrist of either party, willing to tell party leadership to take a hike.

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In his legislative heyday Specter’s fists-first prosecutorial style fit in with a rowdy crowd of centrists who regularly flouted their leadership and, stylistically, sought the glare of national media attention.

They were senators like John Warner (R-Va.), who squired Elizabeth Taylor around Washington while cutting deals on Pentagon funding; the late John Chafee (R-R.I.), whose Marine Corps heroism made him the barrel-chested leader of a rump bipartisan budget group; and John Breaux (D-La.), Chafee’s frequent legislative partner who skipped the 2004 Democratic convention keynote address by Barack Obama to throw a retirement party with Ziggy Marley and several thousand pounds of imported sand on the back lot of Boston’s aquarium.

Those senators are long gone now as the number of moderates has steadily shrunk, with six more pending retirements from centrist ranks at the end of this year. Just as important has been the diminished stature of those centrists left behind.

There are still enough moderates, along with some maverick-leaning conservatives, who could seemingly shift the legislative calculus on almost any issue if they were willing to buck Majority Leader Harry M. Reid (D-Nev.) or Minority Leader Mitch McConnell (R-Ky.).

Instead, more often than not, the Democratic caucus goes along with Reid’s record-level use of parliamentary procedures to forbid Republican amendments, and then the GOP caucus goes along with McConnell’s demand for party unity with a record-level use of the filibuster to block Reid.

Today’s heirs to Chafee-Breaux are Sens. Mark Warner (D-Va.) and Saxby Chambliss (R-Ga.), who have for nearly two years led a bipartisan group trying to negotiate a broad tax-and-spending deal to trim federal debt by $4 trillion. They have not been able to move beyond a vague outline, without an actual legislative draft.

Today’s moderate crowd tends to run from the media glare that predecessors like Specter savored, fearful that getting too far publicly astray from their party’s roots could lead to a primary challenge.

Specter was always aware of such a primary challenge, but he never feared the battle.

“I wasn’t sent to Washington to play it safe. I have something to show for what I’ve done,” he said on the 2010 primary night.

His first official stint in Washington came as junior counsel working on the Warren Commission. In his mid-30s, he authored the controversial “single bullet” theory to explain the Kennedy assassination and then spent the next five decades vigorously defending it. “There will be questions about the assassination of President Kennedy for centuries,” he told the Pittsburgh Post-Gazette in 2003. “I’m not reticent about discussing the subject. I have inside knowledge. And being in public life, I have a duty to speak out.”

When Democrats refused him the nomination for Philadelphia district attorney, he ran and won two terms as a Republican. He won his Senate seat on Ronald Reagan’s coattails in 1980, but then spent much of the next eight years fighting with his judicial nominees, sinking the Supreme Court nomination of Robert Bork.

His last term, however, proved to be a long, slow march against a changing political tide that made it difficult for outspoken centrists to win elections. After barely surviving a primary challenge, he coasted to victory in 2004 and, at a press conference the day after the general election, Specter called Roe v. Wade “inviolate.” That riled conservatives, who required him to issue a statement of principles of how he would handle Supreme Court nominees to become Judiciary Committee chairman.

Conservatives then moved to unilaterally change rules to forbid filibusters on all judicial nominees. Warner and a group of 14 moderates ended the stand-off with their deal, one that Specter played an advisory role in.

Once the 2008 elections shrank Republicans down to just 41 seats, the party’s activist base demanded party unity from the outset of President Obama’s tenure. Specter, joined by Maine’s Republican senators, Susan Collins and Olympia Snowe, negotiated with the West Wing to reduce the price tag of the controversial stimulus to less than $800 billion in exchange for their critical support.

By April 2009 Specter had imploded among GOP voters in Pennsylvania as Patrick Toomey (R), now a senator, soared past him. Faced with certain defeat in a GOP primary, Specter went “jury” shopping, in legal parlance, deciding that it would be easier to be a moderate Democrat than a moderate Republican.

Raised politically in an era when party bosses had real power, Specter believed that the endorsements of Obama, Vice President Biden and then-Gov. Ed Rendell could clear the way for him to secure the Democratic nomination.

He spent his final days of campaigning in May 2010 with a handkerchief at his side, frequently wiping his nose from the side effects of chemotherapy during his battle with Hodgkin’s disease. At the time he pronounced himself “fine” and boasted of playing squash nearly every day. Politically, however, he had discovered that his decades of jabbing Democrats as often as Republicans left him without enough support in either party.

“I’ve crossed the aisle perhaps once too often,” Specter said.