On May 16, 2017, the FBI took one of the most extraordinary steps in its history: It opened a full investigation of the sitting American president. Newly declassified documents released by the White House say the bureau asked whether the president “is or was directed by, controlled by, and/or coordinated activities with” Vladimir Putin’s Russia — and whether he “obstructed and/or conspired to obstruct” the FBI’s own investigation. That the FBI had targeted President Trump was reported in 2019. What was missing was the paperwork — the opening document, the names on it, the chain of command. The May 16...