That is, either Trump’s real estate empire has taken large amounts of money from shady oligarchs linked to the Kremlin — so much that they literally own him; or rumors are true that he engaged in sexual misbehavior while he was in Moscow running the Miss Universe contest, which Russian intelligence has on tape and he doesn’t want released; or Trump actually believes Russian President Vladimir Putin when he says he is innocent of intervening in our elections — over the explicit findings of Trump’s own C.I.A., N.S.A. and F.B.I. chiefs.

In sum, Trump is either hiding something so threatening to himself, or he’s criminally incompetent to be commander in chief. It is impossible yet to say which explanation for his behavior is true, but it seems highly likely that one of these scenarios explains Trump’s refusal to respond to Russia’s direct attack on our system — a quiescence that is simply unprecedented for any U.S. president in history. Russia is not our friend. It has acted in a hostile manner. And Trump keeps ignoring it all.

Up to now, Trump has been flouting the norms of the presidency. Now Trump’s behavior amounts to a refusal to carry out his oath of office — to protect and defend the Constitution.