Scarcely two weeks after the Mueller report dropped, it isn’t clear how the Russia collusion story ends. Will it be limited to the central finding of the report, confirming that Donald Trump and his campaign did not conspire with Russians? Or might it turn out to be something more ironic—for example, criminal prosecution of Justice Department and FBI officials who led us down the collusion path?

Nothing quite concentrates the Beltway mind like an indictment. But what we’ve already learned about the FBI and Justice ought to...