Now there are seven

Pennsylvania — Republican Sen. Rick Santorum
Rick Santorum, one of the most conservative Republican senators, remains the most vulnerable incumbent of either party. There has been no shortage of polling in this Pennsylvania race: Santorum continually hovers around 40 percent, despite his intense advertising. In 10 polls taken since Labor Day, Santorum trailed state Treasurer Bob Casey Jr., the Democratic nominee, by an average of 10 points.

Casey has run an interesting campaign: He has worked hard not to engage Santorum. According to reporters covering the race, Casey's schedule of campaign events is not nearly as full as might be expected for a serious challenger. And he has turned down Santorum's entreaties for more debates. In short, Casey's goal seems to be to avoid making news. Although this has frustrated political observers who had been counting on a bare-knuckled brawl, voters don't seem to care, making it a pretty successful strategy. If there is one thing that Casey understands, it is that this race isn't about him. The more his campaign can keep the attention focused on Santorum, the better off Casey is.

If there is anything that Santorum and his campaign understand, it is that it's hard to draw contrasts with an opponent who refuses to spar with you. This has left Santorum with little else to do but accuse Casey of avoiding the issues and not showing up for work as state treasurer. Given Santorum's own problems, he is not making much progress.

It is very hard to see how Santorum could turn the situation around and win a third term.

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