WASHINGTON — Revolutionary hero Patrick Henry knew this day would come. He might not have anticipated all the particulars, such as the porn actor in the hotel room and the illicit payoff to keep her quiet. But he feared that eventually a criminal might occupy the presidency and use his powers to thwart anyone who sought to hold him accountable. “Away with your president,” he declared, “we shall have a king.”

That was exactly what the founders sought to avoid, having thrown off the yoke of an all-powerful monarch. But as hard as they worked to establish checks and balances, the system they constructed to hold wayward presidents accountable ultimately has proved to be unsteady.

Whatever rules Americans thought were in place are…