It's an older movie, 60's-70's.
It's about A US prsident who slowly goes insane and starts killing citizens (Hippies and such) and the assistant to the president who realizes the president has gone mad. What the assistant does is put a bomb in his fake leg in an effort to assasinate the president and the presidnets cabinet. The assistant (I think but don't know for sure) is, or looks like Walter Mathau ????
Perhaps HAIL (1973)
http://www.imdb.com/title/tt0067174/combined
That may be it !!! Thanks
Qualified as the O.P.'s reply may be, I think it expresses sufficient satisfaction to close the book on this one and move it Solved...