The president is not, of course, above the law, but there are certainly complications in how the law applies to him. In his official actions, he is subject to familiar checks and balances, including the possibility of judicial review of his decisions. The more immediate problem is how a president might be held accountable if he were to commit a criminal offense. The president is not immune from criminal liability simply because he is president, but I do think that criminal prosecution would be incompatible with the president fulfilling the duties of his office. I would assume that impeachment and removal would proceed quickly if there were substantial evidence that the president had committed a serious crime, and that prosecution in the ordinary courts would soon follow.

In President Trump’s case, there are more thorny issues regarding whether the exercise of his constitutional powers can give rise to criminal prosecution for obstruction of justice. No doubt a president could obstruct justice in myriad ways, but it is not at all clear that it could be a criminal act for the president to exercise his lawful power to direct a federal prosecutor to end an investigation or to remove a subordinate executive officer from his duties. The power of the president to pardon individuals for federal criminal offenses has generally been regarded as unreviewable and completely subject to his own discretion. The president could surely issue a valid pardon to his own associates (though abusing his pardoning power might itself be an impeachable offense). It is less clear that the president could issue a pardon to himself. Conceptually, the pardon is an act of mercy, and that would seem to imply that it is only possible to bestow mercy on someone else and so there is an implicit bar against a self-pardon. Certainly, attempting to do so could be regarded as an impeachable offense as an abuse of power, but whether a court should ultimately respect the validity of such a pardon is a much more difficult question.