Updated: 4:14 p.m.Sen. Arlen Specter (Pa.), in explaining his decision to join the Democratic Party on Tuesday, said the Republican Party’s shift to the right and eschewing of moderate lawmakers drove him to abandon its ranks.“As the Republican Party has moved to the right, I have found myself increasingly at odds with the philosophy of the Republican Party and more in line with the philosophy of the Democratic Party,— Specter said during a press conference, adding that after reviewing recent polling data he came to the decision “that the prospects of winning a Republican primary [are] bleak. … I’m not about to have my 29-year record in the United States Senate decided by the Pennsylvania Republican Party.—Specter, who is up for re-election in 2010 and faced a tough challenge from conservative Republican Pat Toomey, repeatedly told reporters that he would “not be an automatic 60th vote— for Democrats. He added that he arrived at his decision after a five-year lobbying campaign by top Democrats, including Majority Leader Harry Reid (Nev.), President Barack Obama, Vice President Joseph Biden and Pennsylvania Gov. Ed Rendell.“I’ve had overtures from many of the Democratic leaders … overtures [that] have gone on for the last five years,— Specter said, adding that Obama, Reid and Rendell have committed to campaign for him and that an official endorsement by party leaders could be in the offing.Republicans, meanwhile, attempted to paint Specter’s defection as purely political, one that he arrived at to ensure his Senate survival. They insisted Specter’s decision should not reflect poorly on the future of the GOP.“This is not a national story, this is a Pennsylvania story. This is a Pennsylvania story about his inability, according to his pollster, to be re-nominated by the Republican Party or to be elected as an independent,— Senate Minority Leader Mitch McConnell (R-Ky.) said on Tuesday. And while McConnell acknowledged that the GOP has struggled to field viable candidates outside the South and parts of the West in recent years, he rejected the notion that the party has drifted too far from the center.“We have not done very well in the Northeast the last couple of years. We haven’t done as well many places as we would like to have done in the last couple of years. … We intend to be competitive on a nationwide basis. I do not accept that we’re going to be a regional party. And we’re working very hard to compete throughout the country,— McConnell said.Specter told reporters that under a deal with Reid, he would maintain his Senate seniority, ensuring he would remain one of the most senior members of the Judiciary and Appropriations committees. However, Specter said it remains to be decided whether in 2010 he will take control of the Appropriations Subcommittee on Labor, Health and Human Services, and Education, which is chaired by Sen. Tom Harkin (D-Iowa).Reid, however, said no changes to Senate committee or subcommittee makeups would be forced on any Members and would be voluntary. “Sen. Specter knows that no one will be dumped off a full committee or subcommittee except on a voluntary basis,— Reid explained. Reid also tried to strike a measured tone on the news overall, calling Specter’s decision a personal one. “This is not a time to gloat or give high-fives. It’s a time to consider a person who’s taken an extremely difficult step,— Reid said.But even as top Democrats welcomed Specter into the fold and signaled they were ready to line up behind him in next year’s election, his party switch did not immediately clear the Democratic field for his seat.Rep. Joe Sestak (D-Pa.), who had been considering the Senate race, continued to leave the door open to running in an interview Tuesday afternoon with MSNBC. “I’m going to have to wait,— Sestak said. “Because if the alternative is Toomey, that’s one issue.—Sestak — who had $3.3 million in the bank at the end of March — added that he would have to “wait and see— how Specter behaves as a Democrat. Any Democrat running against Specter in 2010 would presumably have an uphill battle, given that Obama and Rendell offered to campaign for him. Specter said Rendell even offered to raise money for his campaign. “He said that if I became a Democrat, he would help me raise money,— Specter said. “I said that if I became a Democrat, I wouldn’t need him to help me raise money. I changed my mind about that.—Sestak was considered the most likely Democrat in the Pennsylvania delegation to run in 2010. Fellow Pennsylvania Democratic Reps. Allyson Schwartz and Patrick Murphy had also been considering a bid, but were much less likely than Sestak to actually run.Additionally, former National Constitution Center President Joe Torsella — the only announced Democrat in the race — said in a statement that he was staying in the hunt. “Nothing about today’s news regarding Senator Specter changes that, or my intention to run for the Democratic nomination to the Senate in 2010 — an election that is still a full year away,— Torsella said in a statement. But Specter’s announcement did clear one possible Democratic candidate from the field: State Rep. Josh Shapiro announced Tuesday he would not run, calling Specter “the incumbent Democratic Senator.— Emily Pierce contributed to this report.