Not all Pennsylvania Democrats are down with Arlen Specter. 

Though the party-switching senator has the support of President Obama and Gov. Ed Rendell, at least two potential candidates are leaving open the door to challenge Specter in the 2010 Democratic primary. 

Rep. Joe Sestak, who's been a prolific fundraiser, is considering defying party leaders and running against Specter despite Tuesday's hoopla, though he told FOXNews.com on Wednesday, "I have not made up my mind on it."

Sestak, a second-term House member, is basing his decision on what Specter may do or say in the coming days. Sestak said he wants to hear Specter make his case to Pennsylvania voters about why Specter now should carry the banner for Democrats after representing the Keystone State as a Republican for 29 years.

"I can't say that he shouldn't be (the nominee)," Sestak told FOX News. "I just don't know. It's wait and see. If he's got it, that's great." 

Sestak released a critical statement about Specter's switch from Republican to Democrat on Tuesday, a day when the rest of Sestak's party was welcoming Specter with open arms. 

The other potential challenger to Specter for the Democratic nomination for senator is Joe Torsella, a former Rendell aide who headed the National Constitution Center and is now chairman of the Pennsylvania Board of Education. 

In a written statement Tuesday, Torsella reiterated that he decided to run for Senate to bring new leadership to the chamber. 

"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," he said. 

His campaign committee has raised close to $600,000 for the seat -- nothing like Specter's $6.7 million, but still a start. 

Larry Ceisler, a former Democratic consultant who heads a Pennsylvania public relations firm, said Specter may be the odds-on favorite for the nomination, but he'll probably draw a challenge. 

"I would be very surprised if Senator Specter runs unopposed in a Democratic primary," he said. He said the big question is whether Specter's competition is token or substantive. 

Sestak is substantive, though an underdog, Ceisler said. 

Specter's move puts Democrats one seat away from a filibuster-proof, 60-seat majority in the Senate, a fact not lost on party leaders. Democratic National Committee Chairman Tim Kaine issued a statement saying he was "thrilled" to have Specter on his side and "he can count on our full support." 

Rendell told FOX News on Wednesday he anticipates every "major Democrat" in Pennsylvania will back Specter. 

"I think he'll wind up being the Democratic (candidate). I have no doubt about that," he said. 

Sestak, though, expressed some concern that Specter's decision to abandon the GOP came after consultation between the senator and the Senate Democratic leadership. Sestak noted that Pennsylvania was left out of the equation. 

"I appreciate and highly respect the Washington political establishment but ... in short, this is a decision that has to be made locally, in Pennsylvania," he said. 

Sestak is a retired Navy Vice-Admiral and is the highest ranking former military officer ever elected to Congress. He's suggested that Specter's decision to morph into a Democrat was based on political opportunism. 

"It was exciting yesterday," Sestak said of Specter's switch. "But tomorrow doesn't mean it's determined by today." 

Ceisler said at least 30 percent of Democratic voters will probably balk at the call to support Specter -- which means that Sestak, if he's the only substantive challenger, would have to attract another 20 percent or more. 

"If there was anybody that was in a position who would at least have some of the resources it would be Sestak," Ceisler said. 

Sestak has $3.3 million on hand in his House fund, enough to kick off a formidable campaign even if the Democratic infrastructure discourages donors from aiding him and encourages them to send money to Specter. 

Sestak told FOXNews.com the money gives him the "flexibility" to spend more time on constituent service and to "do what needs to be done." 

Ceisler had his doubts about Torsella staying in the ring. Rendell reportedly is pushing him to step aside, though Torsella spokesman Mark Nevins said that's not true. 

"No one has spoken to Joe and said you should get out of the race," Nevins said, adding that Torsella intends to stay in. 

In a recent interview with Regional News Network, Rendell made clear he wants an open field for Specter. 

"He'd be unopposed," Rendell said when asked about Specter running in a Democratic primary. "The Democrats in the Senate would welcome him. We in Pennsylvania would welcome him. He'd be basically unopposed for the Democratic nomination." 

FOXNews.com's Judson Berger and FOX News' Chad Pergram contributed to this report.