On the evening of June 16, 1972, a security guard at the Watergate Hotel in Washington, D.C., discovered a piece of tape on the lock of the door that led to the National Democratic Headquarters and set off a chain of events that would, ultimately, bring down the presidency of Richard Milhous Nixon. Afterwards, Americans would wonder why Nixon and the Republican party risked so much on such a minor event when Nixon was leading in the election polls, and the Democratic party was in disarray. Indeed, Nixon would go on to win the presidency by a landslide, with 520 electoral votes. Only 270 electoral votes are needed to win the presidency.

The break-in at the Watergate was only part of a larger campaign designed by Nixon supporters to rattle Democratic candidates and tarnish the reputation of the whole party. This campaign included harassment of Democratic candidates, negative campaign ads, two...