April 28 (Bloomberg) -- Pennsylvania Senator Arlen Specter, an independent lawmaker who long bucked leaders of his Republican Party, said he is becoming a Democrat because his former party has “shifted very far to the right.”

The decision was driven by the “bleak picture” that public opinion polls in his state painted of his prospects for winning the Republican nomination for another six-year term next year, Specter said today. His vote for President Barack Obama’s $787 billion economic stimulus measure earlier this year fueled discontent toward him among many Pennsylvania Republicans.

“I am not prepared to have my 29-year record in the United States Senate decided by the Pennsylvania Republican primary electorate,” Specter told a Washington news conference. “Social conservatives” in the party have made “no bones about their willingness to lose the general election if they can purify the party,” he said.

The addition of Specter to the Democratic caucus, if combined with the seating of Al Franken in Minnesota’s disputed Senate race, would give the party the 60 votes required to break filibusters that can stall legislation.

Still, Specter warned that he would “not be an automatic 60th vote” for Democrats to cut off Republican filibusters. “If the Democratic Party asks too much, I will not hesitate to disagree and vote my independent thinking.” The 79-year-old lawmaker, who has battled cancer in the past, said he is full of “vim, vigor and vitality.”

Card Check Bill

Specter gave no encouragement to organized labor, which voiced optimism that his party switch would boost prospects for a “card check” measure to make it easier for unions to organize.

“I think it is a bad deal. I am opposed to it and would not vote” to advance the measure in the Senate, Specter said.

Still, a 60-vote Democratic majority in the Senate would keep the Republicans from using “knee-jerk filibusters at every whim” to block legislation, said Senator Charles Schumer, a New York Democrat.

Schumer also predicted Franken will be seated in several months. Republican Norm Coleman is appealing to the Minnesota Supreme Court a legal ruling earlier this month that declared Franken the winner by 312 votes in their November contest.

Obama Help

White House spokesman Robert Gibbs told reporters today that President Barack Obama would campaign for Specter if asked. In addition, “If the president is asked to raise money for Senator Specter, we’re happy to do it,” Gibbs said.

Specter, at his news conference, said Obama had promised to help him win re-election as a Democrat.

He also said that for the past five years, he has received “overtures from many of the Democratic leaders on a continuing basis” about switching his affiliation.

Several months ago at an event in Philadelphia, Vice President Joseph Biden, a former Democratic senator from Delaware, and Pennsylvania Governor Edward Rendell urged him to switch. The governor offered to raise money for his re-election, Specter said.

Biden, in a statement today, said, “I welcome my old friend to the Democratic Party. Senator Arlen Specter is a man of remarkable courage and integrity. I know he will remain a powerful and independent voice for Pennsylvania and the country.”

Obama was informed of Specter’s decision during an economic briefing this morning in Washington, said a White House official who declined to speak publicly. Obama called Specter and told the senator, according to the official, “You have my full support” and that the administration was “thrilled to have you” as a Democrat.

Republican Reaction

Republicans accused Specter of putting expedience above principle in switching parties. Texas Senator John Cornyn, chairman of the National Republican Senatorial Committee, said in a statement that Specter’s decision “represents the height of political self-preservation.”

Senate Republican Leader Mitch McConnell of Kentucky said Specter’s switch “sets up the potential for the majority to run roughshod over the minority” in that chamber.

Polls showed Specter, who first won his seat in 1980, losing the Republican primary next year to Pat Toomey, a former congressman. Specter defeated Toomey, 50.8 percent to 49.2 percent, in Pennsylvania’s 2004 Republican primary. In that contest, then-President George W. Bush campaigned for Specter. Always popular with many Democrats in the state, Specter won the general election that year with 52.6 percent of the vote.

Previous Party Switch

Originally a Democrat, Specter became a Republican to run for district attorney in Philadelphia in 1965. Specter made that political shift after concluding the local Democratic “machine wanted a DA it could control,” he wrote in his 2000 book “Passion for Truth.”

Last month, Specter said he wouldn’t switch parties. “I am staying a Republican because I have an important role, a more important role, to play there,” he told The Hill, a newspaper that covers Congress. “The United States very desperately needs a two-party system.”

Republican National Committee Chairman Michael Steele reacted to Specter’s announcement today by saying, “Republicans look forward to beating Senator Specter in 2010, assuming the Democrats don’t do it first.”

Popular in Pennsylvania

Schumer predicted Specter would win re-election as a Democrat “by a wide margin” because “Arlen Specter is very popular in Pennsylvania.”

Schumer, a former chairman of the Democratic Senatorial Campaign Committee, said that over the last year he talked with Specter “several times” about the possibility of switching parties. “I just felt he didn’t feel at home any more” as a Republican, said Schumer.

Specter’s vote on the stimulus bill was his most recent high-profile break with Republican Senate leaders. He opposed Robert Bork’s confirmation to be a Supreme Court justice in 1988, which helped thwart the appointment. He declined to support the Republican effort to remove then-President Bill Clinton from office in 1999 in the Senate trial that followed the House’s impeachment of Clinton. Specter also supports abortion rights.

‘A Long Dialogue’

Senate Majority Leader Harry Reid, a Nevada Democrat, said today he and Specter had “a long dialogue” over the years about his place in the Republican Party. He said Specter informed him of his plans yesterday. “Senator Specter is back where he started, as a Democrat,” Reid said.

Specter said Reid told him that he would retain his seniority, which helps determine committee chairmanships. He noted that his 29 years as a senator put him ahead of Iowa Democrat Tom Harkin, who is chairman of an appropriations labor and health subcommittee. Specter has been the ranking Republican on the panel that oversees government medical research. That is “one of the key interests I have,” he said.

Senator Patrick Leahy, a Vermont Democrat and chairman of the Judiciary Committee on which Specter is the top Republican, said, “I expect him to be as independent as ever.”

“I got the impression” that Specter “felt the Republican Party, great party, had left him, not the other way around,” Leahy said.

To contact the reporters on this story: James Rowley in Washington at jarowley@bloomberg.net; Christopher Stern in Washington cstern3@bloomberg.net

Last Updated: April 28, 2009 17:39 EDT