Has any U.S. President ever appeared on a late-night talk show?

As candidates, sure: Bill Clinton played the sax on The Arsenio Hall Show, both JFK and Nixon were separately on The Tonight Show, Barack Obama was on Letterman. But has any incumbent President ever appeared on such shows? Not that I can think of - does it seem too undignified, maybe? And yet IIRC even Clinton, who discussed his underwear preferences on an MTV program, didn’t.

During their presidency, I’d think it more an issue of not having the time, as well as security concerns, than it being “undignified”. Presidents have often gone on talk shows both before and after their presidencies (Clinton was on The View just a few months ago - Sep. 22 '08) so I don’t see why it would be considered undignified.

Presidents have the time for lots of other things, some of which are considerably riskier than appearing in a closed studio before an audience which can be easily sent through metal detectors. I don’t think that’s it.

I googled and came up empty handed. Seems to just be a campaign thing.

Al Gore was on Letterman while he was Veep. Didn’t seem to think it was too undignified. He even did a TopTen while there.

Bush appeared in an episode of Deal or No Deal last year. Obviously not a talk show (late night or otherwise), but that’s the closest I can think of.

Bill Clinton talked movies (but I don’t think actually reviewed them) on an episode of Siskel & Ebert in February 2000.

Probably dosen’t qualify as a late night talk show, but Nixon appeared on Laugh In.

Did I misremember or did Carter and Clinton appear after they were president?

George W Bush was on Oprah.

I don’t think I’ve ever seen a Greek prime minister on a talk show either. I doubt it is about security concerns. Presidents go to places far less secure than a TV studio.
I guess what they fear most is that the host is going to ask the “wrong” kind of question and corner the president and he’ll appear like a fool on TV.

Not late night, but unheard of at the time.

Nixon was not yet president when he did Laugh-In (September 16, 1968). Though it was unprecedented.

According to IMDb, the Oprah appearance by George Bush was also while on the campaign trail before being becoming president (September 26, 2000).

On a related note, Nixon flew on a regular commercial airline flight while president. I think he flew from DC to his home in CA. It was unannounced and he took his secret service detail with him.

He also had Air Force One flying beside the plane, which kind of negated the point he was trying to make.

Gerald Ford made a cameo appearance on Saturday Night Live in 1976. Ford appeared the night his press secretary, former NBC correspondent Ron Nessen, was hosting.

Candidate Bush was on Letterman in October 2000. There’s an account of it here. What this story doesn’t mention is that during a commercial break, while producer Barbara Gaines was standing in front of the desk and talking to Dave, Bush reached over and used her sweater to clean his glasses without her knowledge. It was caught on tape, and Dave has used it many times since.

Nancy Reagan was on Different Strokes while she was first lady. I think she played herself. Of course she was an actress which is how she met Reagan.

I hear that the California Governor will be in an upcoming action movie with Stallone and others. Only 1 day of shooting, but still…

Resurrecting this thread (which is not very old) because Obama has announced he will be appearing on The Tonight Show this week on Thursday as an acting president.

IMDB lists President Bill Clinton as having appeared on Letterman on May 14, 1997, which of course was while he (Clinton, not Dave) was in office.