Even as Sen. Arlen Specter (Pa.) flaunted the support of Democratic leaders in the wake of his decision to switch parties on Tuesday, some in the party indicated they weren’t ready to step out of the way and line up behind Specter — while Republicans did little to hide their anger and desire to defeat him in 2010.

At a news conference, Specter told reporters that President Barack Obama offered to campaign for him, Pennsylvania Gov. Ed Rendell (D) will raise money for him, and Senate Majority Leader Harry Reid (D-Nev.) will give him his full support as he seeks re-election next year as a Democrat.

Democratic Senatorial Campaign Committee Chairman Bob Menendez (N.J.) welcomed Specter to the party and anointed him as Democrats’ candidate next year.

“I just spoke with the Senator on the phone, told him that I look forward to supporting him and making sure this seat stays Democratic in November of 2010,— Menendez said in a statement.

But while Democratic leaders began to show support for their party-switching colleague, at least two potential primary opponents were more hesitant. Rep. Joe Sestak, for one, is continuing to look at a Senate bid. Sestak — who had $3.3 million in the bank at the end of March — had been considered the most likely Democratic Member to get into the race before Specter’s announcement, although fellow Pennsylvania Democratic Reps. Allyson Schwartz and Patrick Murphy were also looking at running.

In a lengthy statement from his office, Sestak said he questioned Specter’s motivation for switching parties. He did not directly address running for the seat when pressed by reporters.

“In short, I believe that the principles of what he is running for and his commitment to accountable leadership are questions that still need to be addressed,— Sestak said.

The only announced Democrat in the race, former National Constitution Center President Joe Torsella, said he would continue his campaign for now. Pennsylvania Democratic sources said that Torsella had the implicit support of Rendell until yesterday, even nabbing the governor’s media consultant, Neil Oxman, to work for campaign.

According to a source close to Torsella, Rendell did not alert him beforehand about Specter’s switch, and party leaders had not called on Torsella to step out of the race.

“The president hasn’t called Joe,— the source said. “I think if today has shown anything, it’s that you never know what’s going to happen.—

But if Specter has the full backing of his new party’s leaders, it will be difficult for any candidate to mount an effective challenge against him in the Democratic primary.

Larry Ceisler, a Democratic consultant who supports Specter, said he thought it was unlikely that anyone could stand in the way of Specter winning the party’s nod. After all, he said, Specter has always had good relationships with Democrats in the state.

“Nothing really changes here,— Ceisler said. “The only thing that changes here between Arlen Specter being a Republican and Arlen Specter being a Democrat is the letter after his name.—

Specter’s popularity with Democratic primary voters has not been tested, but early public polling in the 2010 Senate race has shown he is much more popular with that party than with self-identified Republican voters.

A Quinnipiac University poll from earlier this year showed Specter with a 41 percent approval rating from Republicans and a 71 percent approval rating from Democrats — his highest rating among Democrats since 2002.

Specter said Tuesday that the Quinnipiac poll was consistent with his campaign’s own polling, which showed he dropped 30 points among Republicans after he voted for the stimulus bill earlier this year.

“The pollster said he’s never seen that kind of precipitous drop,— Specter said.

The Senator’s pollster, Glen Bolger of Public Opinion Strategies, confirmed Tuesday afternoon that his firm had resigned from Specter’s campaign.

Specter also said he was “anxious— to take on his 2004 primary opponent, former Rep. Pat Toomey (R), in the general election.

But according to some Pennsylvania Republicans, it’s far from certain Toomey will be the Republican standard-bearer now that Specter has jumped ship.

“I don’t think it’s impossible that there will be other Republicans not looking at the race now looking at it,— said John Brabender, a Republican consultant who has a long history of working for Pennsylvania candidates.

Recent public polls showed Rep. Jim Gerlach and former U.S. Attorney Pat Meehan trailing state Attorney General Tom Corbett in the 2010 GOP gubernatorial primary, making both of them likely candidates to look at the Senate race. Brabender said that because Meehan is close to Specter, Gerlach would be the more likely choice.

“I would imagine that Jim Gerlach’s phone is ringing quite a bit, particularly from folks from the eastern part of the state,— Brabender said.

Senate Republican leaders blasted Specter’s move as a purely political act of self-preservation and said they look forward to defeating him in 2010, without addressing who their candidate might be.