"I am not prepared to have my 29-year record in the United States Senate decided by the Pennsylvania Republican primary electorate, to have that record decided by that jury," Specter said in a Washington news conference.
Conservative ideologues such as Toomey, he said, "make no bones about their willingness to lose the general election if they can purify the party."
Specter said he made the decision over the weekend after talking with his family and close aides. But prominent Democrats led by Vice President Biden and Gov. Rendell had recently intensified efforts to recruit him. The White House quoted Obama yesterday as promising Specter "my full support."
Specter's famous habit of bucking the party line has irritated Republicans, particularly conservatives, for years. But his crucial February vote for Obama's $787 billion stimulus plan had inspired a new level of anger.
"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.
Specter said he "slept on" his decision Sunday night and informed Senate leaders of both parties Monday evening. An agreement with Senate Majority Leader Harry Reid (D., Nev.) could have him headed for a key committee chairmanship.
Specter's decision shook the Capitol and gave Democrats the chance - assuming a lingering Minnesota race goes their way - to have the 60 votes needed to cut off GOP filibusters. Specter said, though, that "I will not be an automatic 60th vote."
His move also threw into sharp relief the Republican Party's political problem as its moderate ranks dwindle and it battles a popular Democratic president. GOP leaders insisted that polls show that voters value a counterweight to the majority's power.
Elected to the Senate in 1980 on Ronald Reagan's coattails, Specter will actually be moving back to his political origins.
He was elected district attorney in Philadelphia on the Republican line in 1965, though he was a registered Democrat; leaders of the city's Democratic machine at the time did not want to slate him. In 1967, Specter narrowly lost the mayor's race to Democrat James H.J. Tate. At one point, Specter was a mentor to now-Gov. Rendell, a Democrat whom he hired as a prosecutor. The two men have been close for years.
"I'm pleased, and we welcome him to the Democratic Party," Rendell said at an awards dinner at the National Constitution Center last night. "I think he's been a good senator for the people of Pennsylvania who's had to walk a fine line."
Polling aside, Rendell said Specter was shocked by the "viciousness" directed at him for supporting the stimulus plan. "He got such hate and vituperation from the far right in Pennsylvania, I think that just broke his spirit," Rendell said.
Seeking his sixth term, Specter already faced hostile political terrain. With about 200,000 voters switching their registration from Republican to Democrat in the last 15 months, the Pennsylvania GOP electorate is smaller and more conservative than in 2004. Specter's Southeastern Pennsylvania base had at least 85,000 fewer registered Republicans than in 2004, when he barely held on to the party's nomination.
Republicans yesterday cast Specter's move as the crassest of all political moves, aimed at self-preservation.
"Let's be honest: Sen. Specter didn't leave the GOP based on principles of any kind," Republican National Committee chairman Michael Steele said.
Toomey, who lost to Specter in the 2004 GOP primary by 17,000 votes out of more than one million cast, said the move was not surprising on one level.
"Sen. Specter has been a left-of-center politician his entire career, and now he's acknowledging that by switching back to the Democratic Party he once belonged to," Toomey said. But he called the move a "betrayal" to thousands of Republicans who had supported Specter for the more than 40 years he had been with the party.
"He was traveling the state as recently as last week saying he was going to remain a Republican," Toomey said in an interview. "The question on Pennsylvania voters' minds is going to be, How can we trust this guy?"
During his afternoon news conference, Specter acted as if a psychic weight had been lifted from his shoulders, making quips and laughing as he described his decision.
Without the obligation to temper his remarks, Specter ripped the Club for Growth for its role in helping to topple several moderate congressional Republicans.
"There ought to be an uprising; there ought to be a rebellion," Specter said.
Senate Republicans portrayed Specter as the destabilizing force.
"I think the threat to the country presented by this defection really relates to the issue of whether or not in the United States of America our people want the majority to have whatever it wants without restraint, without a check or a balance," Senate Minority Leader Mitch McConnell of Kentucky said.
Specter, who frustrated many Republicans over the years with his independence, warned that Democrats could expect the same thing, saying, "If the Democratic Party asks too much, I will not hesitate to disagree."
He said, for example, that he remained opposed to the so-called card-check bill, which would make it easier for unions to organize - the top priority of organized labor, a key Democratic constituency.
Democrats from Obama on down welcomed Specter to the party. An aide handed the president a note at 10:25 a.m. during his daily economic briefing. It said, according to an administration official: "Specter is announcing he is changing parties."
Seven minutes later, Obama reached Specter by phone. In their brief conversation, Obama told Specter that Democrats were "thrilled to have you," according to an official who heard the call.
Obama would raise money and campaign for Specter if necessary, administration officials said.
Joe Torsella, a former aide to Rendell when he was Philadelphia mayor, has announced he is running for the Democratic nomination for Senate and said in a statement that Specter's decision changed nothing.
Democratic Rep. Joe Sestak, who represents the Delaware County-centered Seventh District, has also been considering a Senate run. He said yesterday that he had not made up his mind but that he "loves" his current job and that Specter's decision would not be a factor in his own.
Specter said that he had not asked Reid, Rendell, or other Democratic leaders to clear the primary field for him to have a clear shot at the party's nomination and that such assurances had not been offered.
"I'm ready for whatever competition comes," Specter said during a conference call with Pennsylvania reporters. "I don't think it's realistic to ask anybody for guarantees on that subject."
State Democratic Chairman T.J. Rooney noted that the official endorsement process was a long way off, but he said in a statement: "The Pennsylvania Democratic Party has a long-standing practice of supporting Democratic incumbents."
In his conference call, Specter looked ahead, with relish, to a possible rematch with Toomey in the 2010 general election. "Anxious is the word," Specter said. "Anxious. I'm anxious to go to that jury."
Contact staff writer Thomas Fitzgerald at 215-854-2718 or firstname.lastname@example.org.
Inquirer staff writers Bob Moran and Tom Infield contributed to this article.
In Specter's Own Words
Excerpts from Sen. Arlen Specter's statement and news conference yesterday:
"While I have been comfortable being a Republican, my party has not defined who I am. I have taken each issue one at a time and have exercised independent judgment to do what I thought was best for Pennsylvania and the nation. . . . I now find my political philosophy more in line with Democrats than Republicans."
"I deeply regret that I will be disappointing many friends and supporters. . . . I am also disappointed that so many in the party I have worked for for more than four decades do not want me to be their candidate."
"My change in party affiliation does not mean that I will be a party-line voter any more for the Democrats than I have been for the Republicans."
"Gov. Rendell said if I became a Democrat, he would help me raise money. And I responded if I became a Democrat, I wouldn't need him to help me raise money. I've changed my mind about that, though."
"I have to make a calculation as to whether it's possible, realistic to fight for the moderate wing of the Republican Party in Pennsylvania. And I do not think it's realistic. It's bleak."
Move Puts Heat On Minn. Race
Sen. Arlen Specter's party switch has turned up the heat on Minnesota's long-simmering U.S. Senate race, which now carries the possibility of giving Democrats a filibuster-resistant majority in that chamber.
Specter's turning Democrat means that if Al Franken wins in Minnesota, the Democrats would have 60 seats, raising pressure on whoever loses Franken's grueling court battle over the seat with Republican Norm Coleman to further extend the fight.
Franken emerged from a statewide recount and court challenge with a 312-vote lead, five months after Election Day, but Coleman has appealed to the Minnesota Supreme Court. That appeal is to be heard June 1. Even if Coleman loses, he could carry his appeals into federal courts.
Both campaigns issued careful comments on the Specter news. Campaign manager Cullen Sheehan said Coleman remained focused "on the thousands of Minnesota citizens who have not had their voices heard or their votes counted." Spokesman Andy Barr said Franken "looks forward to working with senators of both parties to make progress on President Obama's agenda and move our country forward."
- Associated Press