The U.S. president has vast constitutional power to grant pardons to people facing possible prison terms even before charges are filed, or to commute the sentences of folks already in jail. President Donald Trump has broached the possibility of using that power to short-circuit the investigation into whether he or his campaign were involved in Russia’s interference with the 2016 presidential election, which he calls a “witch hunt.” Trump has gone so far as to say he can pardon himself, something