Richard Nixon was the 37th President of the United States. On August 9, 1974, Nixon resigned the presidency because of the Watergate scandal.
In the Timeless Universe
In 1972 Washington D.C., Garcia Flynn obtains the deleted eighteen and a half minutes of the famous Watergate tape. Part of the previously missing tape is played to a captive audience of Wyatt Logan, Lucy Preston, and Rufus Carlin. In the tape, Nixon explains that he is being blackmailed by Rittenhouse and that the Doc is missing and needs to be returned.
On July 12, 1969, Nixon makes an appearance on television explaining that the mission to the moon by Neil Armstrong and Buzz Aldrin is in critical condition and that the astronauts will not likely return to Earth.
When a 17-year-old John F. Kennedy's life was in danger in 2018, a half-dollar transformed to show Richard Nixon's face on it, instead of Kennedy's. This implies that for a moment, an alternate timeline where Richard Nixon won the 1960 presidential election. It also implies that Nixon was killed instead of Kennedy, since the half-dollar was from 1964 and living presidents don't get their faces on coins.