This whole thing reminds me a little of David Brock's sudden and idiotic "slide" into leftist politics. Not the same thing, of course, as Tapper has always been a leftist. He tries to make himself appear a little more moderate at times, and can easily fool the stupid out there, but as others have said -- make no mistake about where this guy comes from.
Anyway, if you'll recall, Brock wrote a lot of hard hitting pieces in the American Spectator and the book, The Real Anita Hill (a follow up to his Spectator article by the same name). In it, he decisively proves Hill was lying about her allegations against Thomas. While Brock didn't come right out and say who his sources were, it was clear that he had access, at the very least, to the congressional committee's deposition transcripts of the key witnesses in the case. Simply reporting on that showed, for example, that Hill could not have been referring to Thomas when she allegedly told someone contemporaneously about the harassment since this supposed tale occurred BEFORE Thomas took the job supervising Hill. The person had moved to California and that date had been ironed down. Thus to the extent Hill was telling the truth about being harassed at all (a fair to good possibility), it couldn't have been Thomas. At least not THAT harassment. Otherwise, she was saying that while Thomas DID harass her, the examples and/or proof of that were based on someone ELSE's actual harassment. Either way, it was a little lie or a big lie.
So Brock goes tapioca and tries to claim that he was caught up in a smear campaign and recants most of his previous work. But if you actually read those works, you'd see the cases he built were iron clad and recanting them didn't make any sense. Had they actually been untrue, he, the Spectator and his publisher would have been sued out of existence. Not only were they not, his detractors tried ignoring him and wrote other "books" that were half as long, nowhere near as dense and lacking relevant information, hoping the short attention span of the public would carry the day. People like Jill Abrams weren't interested in the truth, but only in some way to string up Hill's credibility.