WASHINGTON — Sen. Arlen Specter's decision to switch parties Tuesday further erodes the GOP's legislative power and adds a key player to the Democrats' quest for a filibuster-proof majority to propel President Obama's ambitious agenda.
Specter, a moderate who had rejected the antiabortion, anti-spending, pro-gun-rights conservatism that now dominates the Republican Party, said bluntly that he was making the switch because he was facing a stiff primary challenge from conservative former House member Pat Toomey, and concluded that he could only win reelection as a Democrat.
If, as expected, a contested Minnesota Senate election is decided in favor of Democrat Al Franken over Republican Sen. Norm Coleman, Specter would give the Democrats 58 members in the Senate. Adding the two independents who usually align with them would create the 60-vote margin required to block a filibuster -- the minority party's most powerful tool for stalling legislation.
That does not guarantee a sweeping change in the balance of power in the Senate. For example, Specter restated his opposition Tuesday to organized labor's top priority, a bill to make it easier to unionize workplaces. And under Republican presidents, he has supported conservative judicial nominees.
"I will not be an automatic 60th vote," Specter declared.
Still, he has been a reliable ally for Democrats on such matters as health research funding and abortion rights. According to an analysis by Congressional Quarterly, Specter voted with the majority of the GOP in only 62% of party-line votes.
He demonstrated the power of his vote early this year when he provided one of only three Republican votes for Obama's $787-billion economic stimulus bill.
The announcement caught most of official Washington by surprise. Democrats were jubilant, while Republicans insisted it was a matter of Pennsylvania politics, not a sign of a change in national politics.
Nonetheless, Specter's change of party affiliation reflected both his calculation of the present situation in his home state and what Senate Majority Leader Harry Reid of Nevada described as a five-year effort by Democratic leaders to win him over.
Before going public with his decision, Specter won commitments of support from Obama and Reid. Obama said that if asked, he would campaign for Specter in Pennsylvania's Democratic primary -- a venture into local politics that presidents usually avoid because it can lead to bruised feelings and divisions within the party.
The White House commitment, along with Reid's agreement not to penalize Specter in committee ranking, pointed up the Pennsylvania senator's potential value to the Democrats.
At the White House, Press Secretary Robert Gibbs said there had been no deal over the switch, but he added: "If the president is asked to raise money for Sen. Specter, we're happy to do it. If the president is asked to campaign for Sen. Specter, we'll be happy to do it. As the president told Sen. Specter on the phone, he has our full support, and we're thrilled to have him."
As Specter pondered the decision to change parties, the political bind he found himself in was a measure of how much American politics has become polarized by region. The GOP once had a robust wing of moderates -- Rockefeller Republicans, or "Gypsy Moths," who hailed mostly from the Northeast. Now, the party's regional base is largely concentrated in the South and dominated by ideological conservatives.
That shift is part of what Specter said had driven him from the party. "As the Republican Party has moved further and further to the right, I have found myself increasingly at odds with the Republican philosophy," he said.
Specter was primed for a switch six years ago when he faced a brutal primary challenge from Toomey, and eked out a victory -- thanks in part to a big 11th-hour push from President Bush.
His prospects for reelection in 2010 were even grimmer: A recent poll of Republicans found he was trailing Toomey by about 21 percentage points. What is more, his general election prospects as a Republican were clouded by a surge in Democratic voter registration. Since he last ran, about 200,000 Republicans have switched registration.
"It's a bluer state than it was," said Sen. Bob Casey (D-Pa.). "It's the nature of these changing times we live in."
Specter was unabashed in acknowledging that his decision was impelled by poll results late last week.
"I am not prepared to have my 29-year record in the United States Senate decided by the Pennsylvania Republican primary electorate -- not prepared to have that record decided by that jury," he said.
That led Senate GOP leader Mitch McConnell (R-Ky.) to insist that the decision was a reflection of Pennsylvania politics, not a statement on the national state of the party.
Specter's choice was an abrupt switch from just a few weeks ago, when he insisted in an interview that he was running as a Republican to keep Democratic power in check.