Washington Post columnist Marc Thiessen writes:

Last night two centrist Democratic incumbents failed to stave off challenges from the left in Democratic Senate primaries. Pennsylvania Sen. Arlen Specter was defeated by left-wing challenger Rep. Joe Sestak. And Arkansas Sen. Blanche Lincoln was forced into a runoff by her left-wing challenger Gov. Bill Halter.

But don't hold your breath waiting for commentators to decry these shameful efforts at the ideological purification of the Democratic party. When Sen. Bob Bennett is challenged from the right, it is an ideological purge. But when centrists like Specter and Lincoln are challenged from the left, it's democracy in action.

Thiessen's overheated reaction to last night's primary results tell us more about him than about Sestak or Halter. Joe Sestak had the 136th most liberal voting record in the House of Representatives last year. In 2007-2008, Sestak had the 186th most-liberal voting record. That isn't “left-wing” -- not to anyone other than a deeply dishonest torture-loving ex-Bush-speechwriter, anyway. And I'd sure be interested in seeing Thiessen reconcile his derisive description of Halter as a “left-winger” with Halter's election to statewide office in Arkansas.