"This is great news," said Gary Erlbaum, a longtime Specter supporter who backs candidates in both parties. "It would have been very difficult for him to win a Republican primary."
Overnight, the five-term senator who turns 80 next year has gone from being the underdog in a GOP primary to the odds-on favorite to win the Democratic nomination and re-election to a sixth term.
Specter's defection means that U.S. Rep. Eric Cantor (R-Va.) will be the only Jewish Republican lawmaker in Congress.
By returning to the Democratic Party after more than 40 years in the GOP, Specter also becomes a potential 60th vote for Democrats in the Senate.
In a statement released Tuesday, Specter said that his switch does not mean that "I will be a party-line voter any more for the Democrats than I have been for the Republicans."
Still, he expressed his dismay with the direction of the Republican Party: "Since my election in 1980, as part of the Reagan Big Tent, the Republican Party has moved far to the right."
Fans on Both Sides
Specter has long enjoyed strong support in the local and national Jewish community, reaching across party lines for financial support as well as for votes.
Moderates have long hailed him as a reliably pro-Israel lawmaker not beholden to any party. Opponents, particularly on the right, have assailed his failure to articulate and adhere to a political philosophy.
Many Jewish Democrats, even liberals who have disagreed with him on some key issues, lauded his defection -- from President Barack Obama on down.
"This is a great day for the Democratic Party; it demonstrates that we are the party of inclusion, the party that wishes to work with President Obama," said State Rep. Josh Shapiro (D-District 153).
Shapiro, who had been expected to announce his own bid for the Democratic primary, announced Tuesday that he wouldn't run. If he was stung by the fact that the Specter's move had essentially made a victory next to impossible, he didn't express it.
State Rep. Babette Josephs (D-District 182), a Jewish lawmaker who represents the more liberal wing of the party, said that she was delighted "he understands that this is the party that is going to lead us out of all the dreadful economic and international problems that are facing."
Mark Aronchick, a top Democratic player at the state and national levels, said that he had hosted a fundraiser for Specter at his Narberth home just two days before the announcement.
He said Specter hadn't let on then, but Aronchick noted that he had a strong suspicion he'd made up his mind to switch.
"I hope that my gathering showed him the affection that many Democrats have for him," Aronchick said, noting that about 60 people attended, mostly Jewish Democrats.
Mark Felgoise, another political donor who backs pro-Israel candidates in both parties, said, "I am with Arlen Specter whether he is a Democrat or a Republican."
But some of his former Republican allies, not surprisingly, had a very different take.
Steven L. Friedman, co-president of the Republican Jewish Coalition's Philadelphia branch and a longtime Specter backer, said that he was disappointed and still trying to absorb the announcement. Beyond that, he had no further comment.
Kenneth E. Davis, the former Montgomery County GOP chair who has long been active in Jewish affairs, said: "I'm not totally surprised. I'm sort of disappointed that the party can't support people like Arlen Specter; it just doesn't bode well for our party."
Davis, who left his chairman post last year, said that the Republican Party had moved too far to the right on a host of social and economic issues, and that if he were running for office, he might have made a similar decision as Specter.
But Matthew Brooks, executive director of the Washington-baed Republican Jewish Coalition, said that Specter's decision was about political calculus in one race, not about broader trends. He argued that Specter's defection was precipitated by his support for the federal stimulus package, not over a social issue such as abortion or church-state relations.
"We are disappointed that someone who has been a fighter for his views chose to leave the party rather than stay," said Brooks.
Judy Davidson, a supporter of Pat Toomey, the former member of Congress who was leading Specter in the Republican primary fight, said of the longtime senator: "In his heart, he has always been a Democrat on many levels. I think he will be much happier now that he has returned to the Democratic Party.
"For Toomey," she added, "this means game on."