Arlen Specter has long cultivated a reputation as a prickly and pugnacious battler — a survivor of not only two bouts with cancer, but also intense skirmishes with his own party during nearly three decades in the U.S. Senate.
But his long political legacy will likely be defined by his blockbuster decision Tuesday to ditch a flailing Republican Party he says has moved too far to the right and run for re-election in Pennsylvania as a Democrat.
The move was clearly pragmatic, and the Democrats got their newest senator with strings attached.
By becoming the 21st U.S. Senator to switch party allegiance, Specter, 79, will avoid a GOP primary showdown next year that he appeared poised to lose badly. His likely challenger, the conservative former Congressman Pat Toomey, nearly dethroned him in a 2004 primary.
Democratic leaders, salivating at the thought of approaching a filibuster-proof 60-vote majority, have agreed to allow Specter to bring his all-important Senate seniority, and the clout that comes with it, to his new party. And Specter says that the party's biggest star, President Obama, has agreed to hit the campaign trail in Pennsylvania.
"This is a pure political calculation," says Pennsylvania pollster G. Terry Madonna of Franklin and Marshall College. A recent survey by the college showed Toomey getting traction with attacks on Specter's crucial vote in February in favor of Obama's stimulus package.
"He was going to have great difficulty getting nominated in Pennsylvania," Madonna said. "And he has been on this tightrope for a long time."
Stunned Republican leaders raced to define Specter's switch as no reflection on the party, but an act of simple self-preservation.
"This is not a national story, this is a Pennsylvania story," insisted Senate Minority Leader Mitch McConnell.
Texas Sen. John Cornyn, who chairs the committee charged with getting Republicans elected to the Senate and had supported Specter, said that his colleague "wasn't ready to quit so he decided to switch. It's that simple."
But Specter's shift was clearly a punch to the gut of the Republican Party — and a potential boost to Democrats looking for that 60-vote majority in the Senate.
On paper, Specter will be the Senate's 59th Democrat; Al Franken of Minnesota, whose recount win is being challenged in court, is expected to be the 60th.
"Symbolically, this is devastating for Republicans," says Charlie Cook of the Cook Political Report, which analyzes House and Senate elections and campaigns.
"He's doing what it takes to survive, politically speaking," said Cook. "But I also think that Republican Party leaders would be well advised to start preaching a little more political tolerance."
"You'd have to be pretty slow not to understand the consequences Republicans face losing their 41st seat," he said.
But Cook was among those who cautioned against making too much of Specter's potential role in giving Democrats a reliable 60th vote in the Senate — and Specter himself pronounced that "I will not be an automatic 60th vote."
"As a practical matter, it all still depends on the issue," Cook says. "You also have to know what the other moderates are doing," from Democrats Ben Nelson of Nebraska and Blanche Lincoln of Arkansas, to Maine Republicans Olympia Snowe and Susan Collins.
Said Nelson: "The fact that he has switched parties doesn't mean he's going to vote consistently with [the] party line on those votes anymore than it means I'm going to."
Snowe characterized Specter's defection as "disappointing and devastating," a sign, she says, of a GOP that is on its way to becoming a regional party."
She said statements coming from the Republican Party, including Chairman Michael Steele, who characterized Specter's voting record as "left wing," promote a "culture of exclusion and alienation."
"This is a time," Snowe said, "for the Republican Party to re-evaluate and re-define the party."
Some conservatives were more sanguine about Specter's switch, not convinced that will change how he votes. Specter voted with a majority of his Republican colleagues about 65 percent of the time, according to analyses of his record.
Grover Norquist, president of Americans for Tax Reform, said that Specter has never voted for a tax increase and has pledged to maintain his opposition to legislation that would make it easier for unions to organize.
"Obviously, I'd rather have him as a Republican, but when he was a Republican he was an independent cuss, and as a Democrat he'll be an independent cuss," Norquist said. "This won't change where he is on key votes."
Specter, who had been assiduously courted by top Democrats from Vice President Joe Biden to Pennsylvania Gov. Ed Rendell, said it has been his now-former party's inexorable march to the right that prompted his "painful decision."
"I have found myself increasingly at odds with the Republican philosophy and more in line with the philosophy of the Democratic Party," he said Tuesday afternoon, when he declared himself full of "vim, vigor and vitality."
Specter showed palpable disdain for what he described as the "Pennsylvania Republican primary electorate," and said he was not about to let his 29-year record in the Senate be decided by them.
"It is very important to have a two-party system and a moderate wing of a two- party system," he said.
Republican strategist John Feehery says he believes it will be difficult for Toomey to beat Specter in the general election in 2010.
GOP Sen. Lindsay Graham of South Carolina said flatly that Toomey can't win the general election in Pennsylvania and suggested Republicans recruit former Gov. Tom Ridge to run.
Feehery says that Specter's decision to leave the party "wasn't a slap at the Republican leadership, it was a recognition of where the primary voters have gone."
"The Republican Party is going through an ideological cleansing process, and they have to decide whether they want to be a debating society or a political force," Feehery says. "They can't be a majority party without people like Arlen Specter."
Just where he fits in with his new Democratic colleagues and how they react to promises that have been made and are yet to be revealed, remains to be seen.
But for Republicans in Pennsylvania, Madonna says, "this has been a huge, unsettling moment." The same could be said for the national party, despite arguments to the contrary.