“Advertising agencies have tried openly to sell presidents since 1952,” writes Joe McGinnis in The Selling of the President 1968, a chronicle of the attempts to package Richard Nixon to make him more palatable to the American people. Typically, that process of promoting candidates has included a dual-pronged approach: bolstering a politician’s image while also tearing down the character and record of his or her opponents. But with the arrival of the 1970s, the tenor of political advertising suddenly shifted, in no small part thanks to Nixon himself. The Watergate scandal did more than end the Nixon presidency. It made the 70s notable as a decade in which political advertising became overwhelmingly positive. The great paradox of one of the worst presidential scandals of the 20th century was that it forced candidates to stop attacking each other and start persuading the nation that they could be trusted.

Before Watergate, campaign ads often had a hard edge. Nixon, for one, employed a 27-year-old media consultant named Roger Ailes to organize his television strategy, while his campaign crafted a series of jarring attack ads directed by Eugene Jones.

The Jones ads, which featured discordant music and disturbing scenes of bloodshed, and cited alarming statistics including a crime rate that was escalating “nine times as fast as population,” helped secure the election for Nixon. By contrast, ads for Humphrey—including one endorsement recorded by an unenthused Frank Sinatra—seemed to fall flat.

The political ads of the 1970s, by contrast, are notable for their general sense of optimism. Forget fearmongering, or vitriolic attack ads. Instead, politicians just wanted to prove they were regular, true-blue Americans who wanted to put the country back on the right path. “Watergate’s biggest impact actually came in 1974,” says Larry Sabato, a political scientist, and the director of the Center for Politics at the University of Virginia. “The most oft-heard words were ‘honesty’ and ‘integrity.’ Candidates stressed their normalcy. Younger Democratic politicians bragged about their lack of experience in the Washington cesspool, and promised a revolution in DC.” ...