A short essay on political humor by Mark Katz, the author of the very entertaining (and highly recommended) Clinton and Me:

That is why I would urge you to spend your time on the [Delta] Shuttle thinking about candor and not about comedy. Trying too hard to be funny is both unseemly and dangerous. Politicians are there to show that they are in on the joke and that the joke cannot hurt them. By the time the segment is over, all that must be proven is that you (Clark Kent) can sit down with the host (Lex Luthor) and demonstrate that no joke in the world (kryptonite) can harm you.