U.S. Sen. Arlen Specter (D-Pennsylvania) appeared at a convention of progressive bloggers today and was encouraged by his audience to correct statements made by U.S. Sen. Chuck Grassley (R-Iowa) at town hall meetings this week.

After some prodding, Specter agreed to call Grassley today. Later, The Washington Independent’s David Weigel learned that Grassley did not answer Specter’s call, and the Pennsylvania senator who recently switched parties to become a Democrat was forced to leave a voicemail.

But it didn’t end there.

Specter decided to send a public message to Grassley via the micro-blogging site Twitter:

Called Senator Grassley to tell him to stop speading myths about health care reform and imaginary “death panels.”

Grassley has since fired back over Twitter (no word on whether he has also returned the phone call), telling Specter that he never used the term “death panel” but ignoring the larger point:

Specter got it all wrong that I ever used words “death boards”. Even liberal press never accused me of that. So change ur last Tweet Arlen

Both Grassley and Specter are up for re-election in 2010, and both have been threatened from the base of their respective parties over the health reform debate. Specter already faces a Democratic primary challenger, U.S. Rep. Joe Sestak (D-Pennsylvania). Conservatives in Iowa have threatened a similar move against Grassley if he supports Democratic efforts to create a public health insurance option.