Senator Arlen Specter leads Congressman Joe Sestak by 13 percentage points in an early look at the 2010 Democratic Senatorial Primary in Pennsylvania. In June, Specter had a 19-point lead.

The latest Rasmussen Reports telephone survey in the state shows Specter attracting 47% of the vote while Sestak earns 34%. In June, Specter posted a 51% to 32% lead.

Among voters who favor the congressional health care plan, Specter leads 55% to 26%. However, among those who oppose the plan, Sestak leads 61% to 25%.

Statewide, a majority of voters oppose the health care plan. However, 70% of likely Democratic Primary voters favor it. Nationally, support for the plan proposed by President Obama and congressional Democrats has fallen to new lows.

The survey was conducted during a week when Specter has faced some uncomfortable moments in town hall meetings on the health care issue.

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Not surprisingly, Specter, a Republican senator for nearly 30 years who switched parties in April, is much better known than Sestak, a retired Navy admiral and second-term congressman from the Philadelphia suburbs. Specter changed parties out of fear that he would be defeated in the state's GOP Primary by a more conservative challenger. Sestak, who officially announced last week, is challenging Specter, claiming that he is the only true Democrat in the race.

Just 29% of likely Democratic Primary voters now have a very favorable opinion of the incumbent senator. That’s down six points since June. But only 14% have a very favorable opinion of Sestak, down four points from the earlier survey.

The number with a very unfavorable view: 14% for Specter and five percent (5%) for Sestak.

Tomorrow (Thursday), Rasmussen Reports will release general election match-ups featuring Specter and Sestak against the Republicans' likely Senate nominee, former Congressman Pat Toomey.

Specter, a Republican senator since 1981, has always had a difficult relationship with the GOP base. Earlier this year, he was one of only three Senate Republicans to vote for Obama’s $787-billion economic stimulus package. Just after subsequent polling showed Specter trailing by 21 points in a GOP Primary match-up with Toomey, the senator switched parties and became a Democrat.

While Specter was coaxed by senior Democrats to switch with the promise that he would be the party's Senate nominee in 2010, Sestak is bucking his own party leaders to mount a primary challenge. Both Obama and Pennsylvania Governor Edward Rendell have already endorsed Specter and pledged to campaign for him.

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