PITTSBURGH -- He's respected as a prosecutor and legislator -- and reviled as a schemer and political survivor. Twice a Democrat and once a Republican, no one ever said he lacked grit -- or guile. Savvy and scrappy, he is tenacious -- and ubiquitous.

Indeed, with the possible exception of Benjamin Franklin, no one in Pennsylvania history and few in American history have turned up in more places at more opportune times to play more critical roles than Arlen Specter, elected five times a senator and toppled only when he was 80 years old, a survivor of a brain tumor and lymphoma that threatened his life and of multiple tribal rivalries and political wars that threatened his Senate career.

He was born on Abraham Lincoln's birthday in the depths of the Depression, which was peculiarly cruel in the tiny Kansas town of Russell (1930 population: 2,352) where he and his onetime Republican Senate colleague, Bob Dole, were reared. A brilliant student and wily prosecutor, he won a seat on the Warren Commission staff and for nearly a half-century has defended his "single-bullet" theory of the assassination of President John F. Kennedy.

In 1960, Specter ran in Philadelphia for district attorney with city controller candidate Tom Gola, the former La Salle and Philadelphia Warriors star, on one of the great political slogans of the age, aimed at their machine opponents: "We need these guys to watch those guys." Gola holds the NCAA all-time rebounding record (2,201), but Specter holds the Senate all-time rebound record.

Specter was a central player in two Supreme Court blood feuds (over the nominations of Robert Bork and Clarence Thomas) and a presidential impeachment (his inscrutable vote, based on Scottish law, of "not proven" was either an expression of the highest level of the political arts or the most cynical and artful dodge of the age). He was a liberal Republican at a time when that breed was disappearing and a conservative Democrat at a time when that breed was distrusted.

Specter has been a friend of liberal women (he supports abortion rights) and has attracted their ire (for his treatment of Anita Hill during the Thomas confirmation hearings). He's been the scourge of presidents (Ronald Reagan didn't know what to make of him; Bill Clinton didn't trust him) and a candidate for president (he withdrew before any Republican votes were cast in the 1996 primaries).

The Arlen Specter who conceded defeat in Philadelphia Tuesday night to Rep. Joe Sestak looked frail and vulnerable. But throughout most of his career, even in the hard times, he was neither.

He played squash in every city he visited. He was indefatigable. He was Machiavellian. But Cesare Borgia, the hero of Machiavelli's famous tract, had almost nothing on Specter. Indeed, the senior senator of Pennsylvania lived by this precept of "The Prince": "It is better to be feared than loved, if you cannot be both."

Specter's downfall came on a day when a libertarian tea-party insurgent (Rand Paul) named for an objectivist philosopher won a stunning Senate victory against the Republican establishment in a state (Kentucky) that worships hierarchy as much as basketball. It was a day when a Democratic senator (Blanche Lincoln) was forced into a runoff in a state (Arkansas) where a parade of endorsements from the Democratic establishment served only to endanger her renomination.

Lincoln's opponents on the left suggested this slogan for the incumbent: "Blanche Lincoln: Just as she hands her vote to K Street, voting for her hands this seat to the GOP." Therein lies one of the keys to understanding Tuesday's voting: Voters in both parties this spring are more interested in victory than loyalty.

There was, to be sure, a rebellion against incumbents. When things are going wrong, voters naturally turn against the people in charge. It is the principle enunciated by Richard M. Nixon in the 1952 Checkers speech during one of his early crises:

"You have read about the mess in Washington. Mr. (Adlai) Stevenson can't clean it up because he was picked by the man, Truman, under whose administration the mess was made. You wouldn't trust the man who made the mess to clean it up."

Specter was in part the victim of this political impulse, as ancient as the Federalists. But Specter also possessed a fatal combination: He was both an incumbent and an apparent opportunist.

"Why in the world would you think the Democrats would support a man who was a Republican senator for almost 30 years, who supported two Bushes, who supported John McCain against Barack Obama, who embraced Sarah Palin and beat up Anita Hill?" asked Morton Coleman, emeritus director of the Institute of Politics at the University of Pittsburgh. "Why would the Democratic establishment think Democrats had no memory?"

In fact, the Senate primaries in Kentucky and Pennsylvania were ultimately about the same questions: Was the political establishment more interested in politics than policy, and in their maneuvers to retain power were they too cute by half?

In Pennsylvania, Specter waltzed into the willing arms of Democratic leaders desperate for a 60th Senate vote in a chamber riven by partisan rivalry. He had enough liberal bona fides to rationalize his move, but everyone knew there was only one rationale: Specter's survival.

In Kentucky, Senate minority leader Mitch McConnell first pushed Sen. Jim Bunning into retirement and then handpicked Secretary of State Trey Grayson to take his place. Only John Calipari, the wily coach of the University of Kentucky Wildcats, can get away with that kind of mid-game substitution.

So now the son of libertarian icon Ron Paul is the Republican senatorial nominee in a state that since 1952 has strayed from its Republican inclination in presidential elections only four times, and a liberal with a Harvard Ph.D. who once commanded an aircraft carrier group engaged in hostilities in Afghanistan is the Democratic nominee in Pennsylvania. Their opponents made one old-style maneuver too many.