Variety reports that the "rescheduled" appearance of John McCain on David Letterman averaged 6.5 million viewers and a 1.7 rating among 18-49 year olds. Letterman had mocked McCain somewhat mercilessly when he bailed on his previously scheduled appearance. McCain had said that he had to fly out of town, but Letterman caught him being interviewed by Katie Couric in the same building at the same time Letterman's show was being taped.
The 6.5 million was the largest audience for the show since a 2005 appearance with Oprah.
Meanwhile, Joe Biden appeared on The Tonight Show with Jay Leno which averaged 4.6 million.