Richard Nixon did not become president on the strength of his 10th alone. If anything, his 10th is rather problematic (in a certain way similar to Al Gore's). The humongous raja yoga in the 5th house of politics was the driver for his career success. The sign on that 5th house is Sagittarius. The lord of that 5th house is powerful Jupiter, residing in his own house, along with the 9th, 1st and 4th lords. It is no surprise then that Jupiter's subperiod, the final one in Saturn's mahadasa, would take him to the presidency.
Mercury forms part of the rajayoga, though it loses a planetary war to 9th lord Mars. That said, the first years of its period were not unkind. In its own subperiod it gave Nixon one of the greatest landslides in American history, despite Watergate.
Then came Ketu's subperiod. Ketu, itself in a house of Mercury, did not cause his resignation. But next up was Venus. The period began on March 29, 1974. On April 16 came a subpoena for the tapes. May 9th saw impeachment hearings begin, and on July 24th came the Supreme Court's 8-0 decision against the President. August 9th would be the last day of the Nixon presidency.
Saturn in the 10th brought Richard Nixon to incredible heights. At the very beginning of its period he would be elected vice president of the United States. But he would then fail to be elected president in 1960 and even governor of California in 1962. But Saturn is known to give delayed results. In its final subperiod Richard Nixon achieved his greatest ambition.
Venus was lord of a 10th house that contained Saturn. And Venus, from the 7th, was itself afflicted by Saturn. His two great presidential defeats, 1960 and 1974, were marked by Venus' subperiod.
Two postscripts. Saturn rules the 7th house of marriage, not the 10th of the profession, even though it is posited in the latter. Ketu sub Saturn would indeed see the death of his beloved Pat.
And a final postscript. Saturn in a kendra house by its nature either produces men of higher Saturnian qualities (seriousness, discipline, responsibility) or criminals. Richard Nixon, of course, was both.
The other president with Saturn in the 10th was our greatest: Abraham Lincoln.