We already knew that Paul Manafort was in a heap of trouble. It was almost two months ago — July 26, to be precise — that his Virginia residence was raided by the FBI in the predawn hours. As I said at the time, prosecutors do not obtain warrants to toss the homes of people they regard as cooperating witnesses. When they are dealing with cooperators, prosecutors politely request that documents be produced, expecting the witness (and his lawyers) to comply. If some coercion is thought necessary, they will issue a grand-jury subpoena — an enforceable directive to produce documents,...