Specter on Thursday blasted Sestak as a “flagrant hypocrite” for questioning the senator’s bona fides in the Democratic Party, which Specter joined in late April after 28 years in the Senate as a moderate-to-liberal Republican. Sestak has called himself a “true Democrat” and suggested Specter is not.

In a statement released by his campaign, Specter said that Sestak, a retired admiral who was first elected to the House in 2006, didn’t formally affiliate with the Democratic Party until he became a candidate for office and also didn’t vote in many elections.