On a Monday night in September 1964, television viewers watched a little girl counting petals on a flower. Her voice gave way to a man counting down, and then a nuclear blast filled the screen.

The ad ran as a paid spot only once , in support of President Lyndon B. Johnson's reelection campaign. It never mentioned his opponent, Republican Barry Goldwater . The ad played on a fear voters already held, that Goldwater might start a nuclear war . Republicans protested loudly, Democrats pulled the spot, and the uproar got it rebroadcast in full on network news.

I study how emotional appeals persuade, from how viewers' moods shape their reactions to political ads to how anxiety drives people to seek out , and sometimes fail to absorb, information about threats.

The LBJ "Daisy" ad shows why political campaigns to this day continue to reach for fear , and it hints at why the payoff is less predictable than you might think.

Why campaigns use fear

Fear is an alarm . It tells you something threatening is close.…