Updated

Sen. Arlen Specter has lost the trust of Pennsylvania voters after his "betrayal," Former Rep. Pat Toomey told FOX News on Wednesday, saying he's not even certain the five-time senator will be the Democratic nominee after Specter's self-proclaimed hide-saving party shift on Tuesday.

Toomey, who is now the favorite in the GOP primary, said he's "confident" he can represent the state in the U.S. Senate.

"I'm not sure how much Pennsylvania voters are going to trust him," Toomey said. "He just demonstrated that his political career is more important than those principles."

Toomey was narrowly defeated by Specter in the 2004 Republican primary, but Specter's vote in February to support President Obama's $787 billion stimulus bill helped put him 20 points behind Toomey in Pennsylvania Republican primary voter polls.

Specter announced Tuesday that he was switching from the Republican to the Democratic Party, after acknowledging that his prospects for winning next year's GOP primary looked bleak. He added that he found his principles increasingly at odds with a Republican Party he claims has moved to the right.

But a free and clear pathway to the Democratic nomination is not assured for Specter. Democratic Rep. Joe Sestak issued a statement Tuesday suggesting that he is still considering a run in 2010 for the seat Specter has held for nearly 30 years.

"After 31 years in the military, I learned that you run for something, not against someone. Arlen has made a decision to leave a race because he could not win against someone. What needs to be known is what he is running for," Sestak said in a statement.

"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.

Toomey said he's confident he can win the Senate seat regardless of his opponent.

"I'm a Ronald Reagan mainstream Republican ... I got elected three times in a Democratic-leaning district. ... I'm confident I can run statewide," Toomey said.