John McCain (left) and David Letterman
John Paul Filo/CBS
Nielsen Media Research says 6.5 million viewers tuned in for MCain's raincheck appearance.
It was Letterman's biggest night since a December 2005 appearance by Oprah Winfrey, when she laid to rest long-standing rumors of a feud between them, and a boost of 73 percent over the show's average audience this season, the Associated Press reports.
McCain's appearance was a make-up for Sept. 24, when he called Letterman an hour and a half before showtime and said he had to rush back to Washington to deal with the economic crisis.
During that night's show, Letterman ridiculed the GOP presidential nominee and showed him sitting for an interview in New York with Katie Couric instead of boarding a plane.
"I screwed up. What can I say?" McCain said on Thursday night's show.
