John McCain appeared (with Clinton strategist James Carville) in Wedding Crashers (2005):
h/t to TK
And in 2003, CNN reported on Gods and Generals:
Here is Robert Byrd in costume, with visiting Senator Barbara Mikulski (D-MD) and director Robert Maxwell:
When the movie "Gods and Generals" opened Friday, a few lawmakers had more than a passing interest in the Civil War film: They're in it.
Sen. Robert Byrd, D-West Virginia, George Allen, R-Virginia and Reps. Ed Markey, D-Massachusetts and Dana Rohrabacher, R-California, as well as former Sen. Phil Gramm, R-Texas, are history buffs and they were eager to leave the political stage, if only briefly, for the hot lights of Hollywood.
None of the men are likely to give stars Robert Duvall or Stephen Lang any competition, but they enjoyed their cameo roles.
"This was an opportunity to participate in making history come alive," said Byrd, a political orator who likes to sprinkle his speeches on the Senate floor with historical anecdotes and references.
Byrd appeared as a Confederate general, Allen a Confederate officer and Gramm, a Virginia delegate to the 1861 succession convention. Markey and Rohrabacher portrayed Union officers.
Here is Robert Byrd in costume, with visiting Senator Barbara Mikulski (D-MD) and director Robert Maxwell:
