A recent Rasmussen poll shows incumbent Rick Santorum slipping well behind challenger Bob Casey in the race for the Pennsylvania senate seat, and people are wondering why. There are several reasons which come to mind, not the least of which is that Pennsylvania is a blue state which is nevertheless pro-life. In other words, a pro-life Republican running against a pro-choice Democrat will attract a lot of pro-life Catholic Democrats, but Casey is also pro-life and that neutralizes much of Santorum's cross-over appeal. Casey will get pro-life votes that Santorum would otherwise have received if any other Democrat were running.
Another major factor in Santorum's decline is that he's only getting the support of 67% of Republicans. This is an astonishing figure, but it makes sense when we remember that Santorum endorsed liberal Arlen Specter in his primary race against conservative Pat Toomey in 2004. This angered a lot of conservatives and convinced them that Santorum is not a reliable political ally. Later, Santorum voted against Tom Coburn's bill that would have substantially reduced a lot of wasteful and unnecessary spending and this further antagonized those Republicans who pay attention to such things.
There's not much Santorum can do to win the allegiance of pro-life Democrats, but he can woo back disaffected Republicans. He's only got five months to do it, though, so he better get started.