Paul Waldman: Paul Manafort has flipped. So what happens now?

Once again, Robert Mueller's "witch hunt" has caught itself a witch. And this is a big one, as The Washington Post reports:"President Trump's former campaign chairman Paul Manafort is pleading guilty Friday to two criminal charges under terms of a plea deal that includes his cooperation as a potential witness for special counsel Robert S. Mueller III."The decision by Manafort to provide evidence in exchange for leniency on sentencing is a stunning development in the long-running probe into wheth