George Bush took over from JoAnn Falletta to conduct Stars and Stripes Forever:
"We didn't expect him to know the score so well," Falletta said afterward. "He was not shy about conducting at all. He conducted with a great deal of panache."
I will ask a question though. Is it possible the President had any musical training as a kid? That never occurred to me. A quick check of Kitty Kelley's The Family doesn't indicate anything. The Cambridge History of Twentieth-Century Music doesn't answer the question directly but does describe recent presidential interest (and disinterest) in classical music.