In Arkansas, Sen. Blanche Lincoln, a Democrat, is in a fight for her political life even though she is backed by President Obama. In Kentucky, Republican Trey Grayson is in trouble, despite backing from Senate Minority Leader Mitch McConnell, former Vice President Dick Cheney and former New York City Mayor Rudy Giuliani.
Many have cited Sen. Scott Brown's upset of Democratic candidate Martha Coakely in the January special election for the Massachusetts Senate seat of the late Ted Kennedy, partly out of concern that history might repeat itself in November if the Democrats are coming off a rough primary season.
But Sestak said a rigorous primary is good for Pennsylvania, pointing to the 2008 presidential primary season.
"This primary, as it did for Obama and [Hillary] Clinton, strengthens candidates. We're a hard, tough, smart crowd here in Pennsylvania. Going through this process helps you," he said. "It certainly helped me. It has taught me a lot."
Pennsylvania was considered a barometer for national sentiments in the 2008 Presidential election. Often considered a possible swing state, Pennsylvania holds a large middle class constituency, one that has felt lasting repercussions of the recession. Once a national leader in job creation, the state faces a 9.4 percent unemployment rate, in line with the national average.
Elsewhere in Pennsylvania is the first big test of Republican efforts to win back the House: a special election to replace long-time Democratic Rep. John Murtha, pitting Republican Tim Burns against Democrat Mark Critz.
Both parties brought out heavy-hitters. Bill Clinton stumped for Critz over the weekend; Scott Brown campaigned for Burns. Yet, as in the Senate Democratic primary, the race is also too close to call.
With the primary just days away, both Specter and Sestak will hit the ground in Pennsylvania, talking directly to the voters about jobs, about healthcare, and the host of issues that are central to their lives and their choice on the ballot.
Both candidates are campaigning hard until the very end, and have said they will remain in Pennsylvania through Tuesday's election results.
Come Wednesday morning, whoever wins starts the next battle, against Republican candidate Pat Toomey.
Quinnipiac polls puts Toomey ahead of Specter 47 percent to 40 percent. Against Sestak, the margin is 42 percent to 40 percent.