Scenes from the Pennsylvania Senate Race

Pennsylvania Senate Race
Mark Peterson / Redux for TIME

Democratic Challenger
Recruited by the Democrats back when Specter was still a Republican, retired Navy Admiral Joe Sestak has provided a threat to him from the left. Though he underperforms the incumbent in polls, Sestak has the potential to draw the liberal Democratic base away from him in the May 18 primary.

Get the Latest Photos from Time.com
Get TIME photos and pictures of the week delivered directly to your inbox.