Among those inclined to believe Specter switched because agrees with Democrats more on the issues, he trumps a potential Democratic challenger by 56 points, 74 - 18 percent. However, among those who believe Specter's primary rational was political expediency, he trails a generic Democratic candidate by 32 points, 28 - 60 percent, suggesting that should more primary voters come to believe that Specter won't be a Democrat when it counts, the race could dramatically shift away from him.
When more Pennsylvanians believe that Arlen Specter switched parties to win re-election, his chances of victory decline rapidly. That is a pretty easy case to make, since Specter said as much back when he switched.
This ad, which is backed by a large monetary buy, twice shows Specter himself saying that he switched parties to win re-election. Showing him with Bush and Paalin won't help much, either. In fact, the praise from Bush could easily cancel out Specter's ads with Obama's praise, since that just emphasizes Specter's self-interested sucking up to power.
Even before this ad, Specter was already in a lot of trouble. The four polls taken entirely since Sestak started running paid media average to 46.0%--40.8%. The rapid shift toward Sestak reveals what was always Specter's underlying weakness in the campaign: Sestak has long led among Pennsylvania voters who are aware of both candidates. Even without more Pennsylvanians believing that Specter switched parties to save his job, Specter still could have lost the campaign if Sestak's name ID rose high enough (which the bio ad and relentless campaigning is accomplishing).
Finally, that last point underscores how expected low Democratic turnout could doom Specter once and for all. Democratic turnout is way down in primaries this year, compared not only to 2008 but also to 2006 and 2002. Lower turnout is going to increase the percentage of news junkies in the electorate, and thus the name ID of Joe Sestak in the electorate. As such, it is entirely possible that Sestak is already ahead among the people who will actually vote. Current polling may be picking up a broader range of voters who are lower information, who don't know Sestak, but who won't show up on May 18th.