No, not Sen. Hillary Clinton (D-NY). She has other things on her schedule in her quest for the White House. It is her husband, former President Bill Clinton, who is going to be sitting in the guest chair a week from tonight on CBS’ "Late Show with David Letterman." He is out promoting his latest book, "Giving: How Each of Us Can Change the World," although he might slip in a pitch for votes for the missus. This will be the 4th appearance by President Clinton on Letterman’s show.