WASHINGTON—On Monday, the Supreme Court issued a decision in Donald J. Trump v. United States. The ruling gives a president immunity from prosecution for crimes committed through official acts as president. For some acts–for powers the Constitution gives only to the president–the immunity is to be “absolute.” For other official acts, the ruling gives the president a rebuttable presumption of immunity from criminal liability. To hold a president accountable for such crimes, the prosecutor would have to show that the prosecution would not intrude on the authority and functions of the Executive Branch. In shielding a…