Because this is heading to a holiday weekend, CNN is opting not to present an original installment of its newest documentary series. That’s the bad news. The good news is that, starting tonight at 9 p.m. ET, it’s repeating the three episodes televised so far: on television, Watergate, and the Vietnam War, respectively. Oh, and consider this a warning, as well as a recommendation: In the first part, on television in the Seventies, I appear on camera from time to time. But watch it anyway…