Michael Cohen’s decision to plead guilty to lying to Congress on Thursday was remarkable for three reasons.The first was that Cohen walked into a Manhattan federal courtroom unannounced. He did it by surprise. We live in a political environment characterized by constant leaks, each choreographed more carefully than a public announcement. The drama of learning what’s going to happen at an event, rather than before the event, has mostly disappeared. But Cohen’s plea, a momentous development in Special Counsel Robert Mueller’s investigation, happened with no warning. That reflects admirable discipline in Mueller’s office.