HARRISBURG -- Republican Senate candidate Pat Toomey thinks Sen. Arlen Specter has "a big problem" in both a Democratic primary for Senate and the general election in 2010.

By switching from the Republican Party to the Democrats -- after many times saying he wouldn't -- the longtime incumbent has raised the issues of credibility and trust, Mr. Toomey told the Pennsylvania Press Club today.

"He's introduced a huge question about whether he can be trusted,'' the former three-term congressman from the Lehigh Valley said. "He crisscrossed the commonwealth repeatedly insisting he was not going to leave the Republican Party, that he would stay in the party to the end.

"(He said) that it was vitally important that Republicans retain 41 votes (in the Senate) to provide a check on unlimited Democratic control. Then he took one look at a poll, saw that he probably couldn't win (the GOP primary in 2010) and broke his word. I think that Democratic voters will ask themselves -- if Republicans couldn't trust him, why can we?"

Mr. Toomey, 47, former head of a conservative group called the Club For Growth, said he'd expected "to beat Arlen Specter soundly in the Republican primary, but I had no idea I would drive him clear out of the party.''

Mr. Toomey also criticized Mr. Specter for saying that when Mr. Toomey was working in the financial industry on Wall Street, he sold risky investments called "credit default swaps,'' which are blamed for contributing to the recession in the housing industry.

"In fact,'' Mr. Toomey said, "I'd left the financial industry before they were even invented.''

Without knowing exactly who he'll face in either the 2010 primary or the general election, Mr. Toomey said he's confident he'll win both elections.

So far, social conservative Peg Luksik of Johnstown is also seeking the GOP Senate nomination, and U.S. Rep. Jim Gerlach of suburban Philadelphia has been mentioned as a possibility. Larry G. Murphy, a Philadelphia native and Air Force veteran who now has a communications business in Hermitage, Mercer County, is also seeking the GOP nomination.

On the Democratic side, U.S. Rep. Joe Sestak of suburban Philadelphia could be running against Mr. Specter in the May 2010 primary. And state Rep. Bill Kortz, D-Dravosburg, has said he is running in the primary.

Mr. Toomey, a fiscal conservative, is generally seen as the favorite in the GOP Senate primary. But some commentators think he may be too conservative to win the general election, since Democrats lead Republicans in voter registration about more than 1 million voters.

Mr. Toomey disputed the idea he can't win a general election, saying he won three times in the Lehigh Valley, which has a lot of Democratic voters, and insisting his ideas of limited government and low taxes will resound with voters.

"I'm not going to change the fact that I think the government spends too much money and ought to spend less,'' he said. "I think taxes are too high. I don't think taxpayers should be forced to bail out failing companies. We need someone to be a check to (Democratic leaders like) Sen. Harry Reid and Rep. Nancy Pelosi.''