I first met Joe Sestak in 2006 when he was campaigning for a House seat in suburban Philadelphia against a ten-term incumbent. Few thought, originally, that he could win, but he persevered—like a typical Navy man—and after his opponent self-imploded Sestak cruised to an easy victory. That race in 2006 should’ve taught Arlen Specter not to underestimate his primary opponent in 2010. Sestak knocked off Specter tonight in an unpredictable Democratic primary, 53 to 47 percent at last count.

Virtually every powerful Democrat, from Barack Obama to Pennsylvania Governor Ed Rendell to the AFL-CIO, urged Sestak not to challenge Specter after the incumbent switched parties to run as a Democrat. A few months ago he was down by thirty points in the polls. But the Tea Partiers aren’t the only ones who are tied of being told what to do by their party establishment. Sestak scored a dramatic comeback by capitalizing on the rising angst among the Democratic base, tying Specter to his former Republican friends like George W. Bush and Sarah Palin, and highlighting the fact that Specter opposed Elana Kagan’s nomination as solicitor general and often couldn’t seem to distinguish between Republican and Democratic crowds. Specter’s forty years of Republican baggage ultimately proved too much of a weight for Democratic voters to bear. Sestak’s last ad, in particular, was devastating for Specter.

 “This is what democracy looks like,” Sestak said at his victory party, mentioning how he triumphed “over the establishment, over the status quo, even over Washington, D.C.”

Meanwhile, the race in Arkansas between Bill Halter and Blanche Lincoln—where some thought Lincoln might get over 50 percent and score a clean victory—is still too close to call. That likely portends well for Halter if the race goes to a runoff. It’s been a good night for the insurgents, so far.