Sen. Arlen Specter's likely challenger in the 2010 Pennsylvania Senate race is gaining ground but still trailing following Specter's switch to the Democratic Party, according to a new poll. 

A Quinnipiac University poll showed former Rep. Pat Toomey trailing Specter by 9 points, 37-46 percent, in a hypothetical general election. 

That's better than Toomey's showing in a May 4 poll, in which he trailed Specter by 20 points immediately following Specter's party switch -- a switch Specter decided to make in large part because polls showed Toomey beating him in the GOP primary race. 

The numbers and candidates in the Pennsylvania race are still in a state of flux. Former Republican Pennsylvania Gov. Tom Ridge was considered a possible challenger, but he opted not to run earlier this month despite a Quinnipiac survey showing him competitive against Specter in a general election. 

Now Toomey is the leading GOP candidate. Another potential Democratic challenger recently dropped out of the race against Specter as well. 

And though Rep. Joe Sestak, D-Pa., is expected to challenge Specter in the Democratic primary, the latest Quinnipiac poll shows the lesser known congressman trailing the five-term senator by nearly 30 points.