Trump’s Attack on Ontario’s Reagan Ad Helped Amplify Its Reach

In the global portfolio of political ads that changed history, a handful stand out.

In the UK, the famed “Labour Isn’t Working” poster of 1978 has long been credited for helping Margaret Thatcher’s Conservative government sweep to power the following year. Before that, the “Daisy” political ad, created for US President Lyndon B. Johnson’s campaign against Barry Goldwater, was pulled from the air for fear-mongering in 1964 — but also deemed tremendously effective.

And late Thursday night, a 60-second spot from Ontario, Canada, based on excerpts from a 1987 radio address by former US President ...