On tonight's 20/20 — airing 10 pm/ET on ABC — Barbara Walters quizzes CBS Early Show host Bryant Gumbel about quitting morning TV. "It is probably harder to walk away from failure," he admits, "and I guess some people would argue this was! But in this instance, it's just the right thing to do." The divorcé also denies committing adultery with his current fiancée — and explains that famed friction with his old Today co-host Katie Couric. "I don't know if I'd call it tension," Gumbel hedges. "Katie and I were never really close."