In 1973, the possibility loomed that President Nixon and Vice President Agnew could face criminal charges at the same time while holding office. In the first opinion of the Justice Department’s Office of Legal Counsel, Assistant Attorney General Robert Dixon explained how the President’s unique role provided immunity until he left office.

Dixon said a sitting President should be barred by the doctrine of separation of powers from a criminal indictment and trial that would “unduly interfere in a direct or formal sense with the conduct of the Presidency.”

“An impeachment proceeding is the only appropriate way to deal with a President while in office,” Dixon concluded, noting the potential effect on the overall Executive Branch.

The Constitution's Article II, Section 4, spells out that, "The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors."

Two weeks after Dixon’s memo, a second one followed from Solicitor General Robert Bork about the Vice President Agnew’s immunity request from criminal charges while in office. Bork offered a textual explanation about why only the President would enjoy such short-term immunity.

“The President’s immunity rests not only upon the matters just discussed but also upon his unique constitutional position and powers,” Bork wrote. “There are substantial reasons, embedded not only in the constitutional framework but in the exigencies of government, for distinguishing in this regard between the President and all lesser officers including the Vice President.”