[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2009/images/10/14/art.getty.arlen.specter.jpg caption="Republican challenger Pat Toomey leads Sen. Arlen Specter of Pennsylvania by double digits in a possible November showdown, according to a new poll."](CNN) - Republican challenger Pat Toomey leads Sen. Arlen Specter of Pennsylvania by double digits in a possible November showdown, according to a new poll.
A Franklin and Marshall College survey released Wednesday indicates that 45 percent of likely voters back Toomey, with 31 percent supporting Specter and 20 percent undecided.
Polls conducted last October and December suggested Toomey, a former congressman and former head of the Club for Growth - a limited-government and anti-tax organization - and Specter were deadlocked. Specter, a five-term senator, switched parties from Republican to Democrat last spring, saying at the time that the difficulty in winning the Republican primary was a factor in his decision.
According to the Franklin and Marshall poll, the race between Specter and Toomey is deadlocked at 30 percent each when all registered adults are included in the survey, with more than a third undecided.
The poll also indicates that Toomey leads Rep. Joe Sestak 41 percent to 19 percent among likely voters in a hypothetical general election matchup, with 37 percent undecided.
Among all registered voters, Toomey leads 28 percent to 16 percent with more than half undecided.
Sestak, a two-term congressman from southeastern Pennsylvania and former Navy admiral, is challenging Specter in May's Democratic primary. According to the poll, Specter leads Sestak 30 percent to 13 percent among likely Democratic primary voters, with half of those questioned undecided.
The Franklin and Marshall College poll was conducted January 18-24, with 993 registered Pennsylvania voters questioned by telephone. The survey's overall sampling error is plus or minus 3.1 percentage points.
- CNN Deputy Political Director Paul Steinhauser contributed to this report