Mr. Trump’s mental health is being questioned because he insists on saying a true thing about the violence in Charlottesville. Even the visible dismay on the faces of his own aides at his Aug. 15 press conference was there because he spontaneously reverted to the truth when they thought they had extorted his promise to refer only to the violence of the white-supremacist groups.

The other thing to notice is that “Trump is a liar,” another favorite media theme (one with considerable validity), has had to be put on hold for the duration.

Mr. Trump is being diagnosed as crazy for insisting on an undisputed fact. Sociologically, this is interesting. A columnist of a more polemical bent might even make reference to the Soviet-era practice of condemning citizens to mental institutions for questioning the lies of the state.