Satchel Paige, the legendary master of the sinking curve ball and famous doctor of philosophy, had a few wise words that Robert Mueller could use just now: “Don’t look back, something might be gaining on you.”

Mr. Mueller seems to be transforming himself from the hunter to the hunted. A mole in the Trump campaign has been exposed as an agent of the FBI despite frantic efforts to keep the scheme a secret. Voices, some of them voices of Democrats, are raised to tell Mr. Mueller that it’s time to put cards on the table, to ring down the curtain, to put up or shut up, choose your cliche.