But Nixon worried that would help elect his rival, Democrat Hubert Humphrey. As Farrell explains, Nixon—a former vice president, senator, and U.S. representative—had a large network of contacts he could draw on to help torpedo the peace talks. Anna Chennault, a Republican fundraiser, had close ties across Asia through her lobbying on behalf of nationalist China. Through her, and with the help of Chiang Kai-Shek, they pressured South Vietnamese President Nguyen Van Thieu to stall talks. Rose Mary Woods, Nixon’s secretary who would later become famous for erasing tapes from the Oval Office, worked another connection. Other elements of the effort were far simpler: Nixon threatened CIA Director Richard Helms with firing if he didn’t cooperate.

In the end, Nixon’s meddling worked, scuttling any peace deal. Perhaps it helped contribute to his victory in the presidential race, too, which he won by less than a percentage point in the popular vote. Whatever the benefit to Nixon, the costs of not ending the war are clear: More than 21,000 Americans were killed in Vietnam between the end of 1968 and the American withdrawal.

The effect of this strange maneuvering was that for a time, foreign leaders were negotiating with two different American heads of state, one elected and one not yet in office, a situation that is now being repeated with Barack Obama and Donald Trump. Nixon’s extensive government experience allowed him to intervene even before he was elected president, while Trump had to wait until after his upset win.

Since November 8, however, Trump has not been shy about jumping in. Lame-duck presidents are not a new phenomenon, and countries have long known that they can slow-walk through the last days of one administration to get to the next. What sticks out about Trump’s pre-presidency is his willingness to break traditions by using the bully pulpit even before he possesses it. He has openly disputed the overwhelmingly assessment of the U.S. intelligence community on whether Russia is responsible for the hacks. When the U.S. government lowered sanctions on the Kremlin over those attacks, Trump all but promised to reverse course once inaugurated. When the UN Security Council considered a resolution condemning Israeli settlements in the occupied territories, Trump first lobbied the U.S. to veto it and then promised things would be different when he came to power.

There’s plenty of space for Trump to continue bedeviling Obama in the remaining few days of his term. The president is seeking to move as many prisoners as possible out of the facility at Guantanamo Bay before he leaves office. Taking prisoners has been a good way to curry favor with Washington for the last eight years, but with Trump noisily backing the facility, would a foreign leader want to take the risk of annoying the incoming president, a man who does not carry a grudge lightly?