Sen. Arlen Specter (D) continues to lead former Rep. Pat ToomeyPatrick (Pat) Joseph ToomeyNewly declassified memos detail extent of improper Obama-era NSA spying Overnight Tech: FCC won't fine Colbert over Trump joke | Trump budget slashes science funding | Net neutrality comment period opens Appeals court decision keeps lawsuit against NSA surveillance alive MORE (R) in his reelection bid but his numbers have slipped some since last month when he switched parties.

According to a Quinnipiac poll released on Thursday, Specter leads Toomey 46 percent to 37 percent. That's down slightly from the 53 percent to 33 percent advantage Specter held in a May 4 Quinnipiac poll.

Specter leads Toomey among Democrats by a 73 percent to 10 percent margin and among independents by a 43 percent to 33 percent margin.

Quinnipiac also tested a match up between Specter and Rep. Joe Sestak (Pa.) in the Democratic primary. Sestak, who said Wednesday night that he intends to get in the race, trailed Specter 51 percent 21 among Democrats.

"Sen. Arlen Specter's numbers have slipped since the controversy that followed his switch to the Democratic Party, but he's still better off than he would have been if he stayed a Republican and faced a tough primary challenge from former Rep. Pat Toomey," said Clay F. Richards, assistant director of the Quinnipiac University Polling Institute.

There are some other troubling numbers for Specter in the survey. Respondents were split almost evenly when asked whether Specter deserved to be reelected, with 43 percent saying he does not and 42 percent saying he does.

Specter's job approval numbers have also slid a bit. Just over half - 51 percent - approve of his job performance, while 39 percent disapprove. In the May 4 poll, 56 percent approved of the job Specter is doing, while 36 percent disapproved.

There was a margin of error of plus or minus 3 percent in the poll.