So why is it clear that the president lacks the power to pardon himself? There are three reasons. The language of the pardon power itself is ambiguous in the face of a constitutional expectation of clarity if the Framers intended to invest the president with such extraordinary power — a power in the sovereign that was little known to the Framers, if known at all.
Second, the Framers clearly contemplated in the impeachment provisions of the Constitution that the president would not be able to violate the criminal laws with impunity. There, without so much as a hint of a president’s power to avoid criminal liability through self-pardon, they provided that even “in Cases of Impeachment,” for which the president can only be removed and disqualified from holding high federal office, “the party convicted shall nevertheless be liable and subject to Indictment, Trial, Judgment and Punishment, according to Law.”
And last, but not least, a power in the president to pardon himself for any and all crimes against the United States he committed would grievously offend the animating constitutional principle that no man, not even the president, is above and beyond the law.