At last.

U.S. Sen. Arlen Specter has been defeated in a Pennsylvania primary in his bid for a sixth term after taking the risky step of switching to the Democratic Party.

Voters Tuesday picked U.S. Rep. Joe Sestak as the party’s nominee and rejected the 80-year-old Specter in his first Democratic campaign.

The vote also was a defeat for President Barack Obama, who supported Specter when he abandoned the Republican Party last year.

It’s a pyrrhic victory, arguably, since Sestak actually polls slightly better against Toomey than Specter does and doesn’t have to shoulder the burden of incumbency in this very anti-incumbent year. But (a) with Tim Burns crashing and burning in Murtha’s district, we need some good news tonight, and (b) if you believe this is a GOP year, you shouldn’t fear Sestak in a swing state. It’ll be tight, but Toomey’s a quality candidate. And Specter is way, way, way past his political expiration date.

My friends, our long national nightmare is over.

Update: Enjoy Specter’s humiliation, because in the most important race of the night — the bellwether — the GOP has flamed out.