Donald Trump’s plan to build a wall along the U.S.-Mexico border did not come from security analysts following years of study or through evidence that a wall would reduce illegal immigration. Amazingly, for something so central to the current U.S. president, the wall came about as a “mnemonic device” thought up by a pair of political consultants to remind Donald Trump to talk about illegal immigration.

In 2014, Trump’s plan to run for president moved into high gear. His political confidant was consultant Roger Stone. “Inside Trump’s circle, the power of illegal immigration to manipulate popular sentiment was readily apparent, and his advisers brainstormed methods for keeping their attention-addled boss on message,” writes Joshua Green, author of Devil’s Bargain: Steve Bannon, Donald Trump, and the Nationalist Uprising. “They needed a trick, a mnemonic device. In the summer of 2014, they found one that clicked.”

Joshua Green had good access to Trump insiders, including Sam Nunberg, who worked with Stone. “Roger Stone and I came up with the idea of ‘the Wall,’ and we talked to Steve [Bannon] about it,” according to Nunberg. “It was to make sure he [Trump] talked about immigration.”

The concept of the Wall did not click right away with the candidate. “Initially, Trump seemed indifferent to the idea,” writes Green. “But in January 2015, he tried it out at the Iowa Freedom Summit, a presidential cattle call put on by David Bossie’s group, Citizens United. ‘One of his pledges was, ‘I will build a Wall,’ and the place just went nuts,’ said Nunberg. Warming to the concept, Trump waited a beat and then added a flourish that brought down the house. ‘Nobody,’ he said, ‘builds like Trump.’”