As he resigned from his post Wednesday, former special counsel Robert Mueller explained that “longstanding” Department of Justice policy prevents a sitting president from being charged with a federal crime. Therefore, while his office investigated potential offenses committed by President Donald Trump, charging Trump was “not an option we could consider.”
The policy blocking indicting a sitting president dates back to the presidency of Richard Nixon. In September 1973, just under a year before Nixon resigned, the DOJ’s Office of Legal Counsel determined that a criminal case against the president “would interfere with the President’s unique official duties, most of which cannot be performed by anyone else.” Therefore, impeachment is the only manner by which a sitting president can be penalized for wrongdoing.
This memo—titled “Amenability of the President, Vice President, and other Civil Officers to Federal Criminal Prosecution while in Office”—analyzed historical texts over 41 pages to weigh the pros and cons of charging a sitting president. Upon his conclusion, Assistant Attorney General Robert G. Dixon, Jr. noted “certain drawbacks” to preventing the indictment of a sitting president—namely that the statute of limitations on the alleged crimes could run their course before the president leaves office, creating a “complete hiatus in criminal liability.”
Still, the OLC argued this “gap in the law” is not enough to overcome the downsides to indicting a sitting president, stating “in this difficult area all courses of action have costs.” According to the memo, the president’s role is too vital to be disrupted by criminal charges.
“To wound him by a criminal proceeding is to hamstring the operation of the whole governmental apparatus, both in foreign and domestic affairs,” reads the memo. “The spectacle of an indicted President still trying to serve as Chief Executive boggles the imagination.”
The DOJ reaffirmed its position on the matter decades later, in an October 2000 memo titled “A Sitting President’s Amenability to Indictment and Criminal Prosecution.” This memo ultimately decided the 1973 memo’s reasoning remains true, and “that subsequent developments in the law validate both the analytical framework applied and the conclusions reached at that time.”
The Supreme Court has addressed matters surrounding the indictment of a president since 1973: United States v. Nixon determined that a president’s desire for confidentiality does not outweigh a criminal subpoena for information, Nixon v. Fitzgerald determined a president cannot be tried for civil damages arising from official conduct, and Clinton v. Jones determined certain civil proceedings unrelated to the presidential office can be taken up against a sitting president.
The Supreme Court has yet to determine whether a sitting president can be criminally indicted, however, leaving the 1973 and 2000 DOJ memos as the only enforceable regulation.
The Constitution, for its part, does not address the possibility of criminal charges against a sitting president. It only asserts that the president can be impeached for “Treason, Bribery, or other high Crimes and Misdemeanors”—and only the House of Representatives has the power of impeachment.
Mueller said Wednesday that “the Constitution requires a process other than the criminal justice system to formally accuse a sitting president of wrongdoing,” which many Democrats have called a referral to Congress to take action against Trump in the form of impeachment.
More must-read stories from Fortune:
—Robert Mueller resigns, says charging Trump with crime was ‘not an option’
—Pelosi says Trump is becoming ‘self-impeachable’
—What would impeachment look like in Trump’s America?
—Rep. Rashida Tlaib is unapologetic about her expletive-filled call for Trump’s impeachment
—Trump tweets that Democrats want to impeach him for being ‘too successful’