On Tuesday, he wrote The Washington Post a memo outlining how he would compel Mexico to pay for what he’s described as a 1,000-mile-long wall at the Southern border—a plan that has sat at the core of the candidate’s campaign since his very first speech.

The memo, titled “Compelling Mexico to Pay for the Wall,” proposes forcing immigrants to prove their legal status before they can wire money to relatives abroad, as well as canceling visas and jacking up visa fees. Trump’s memo proposes threatening the Mexican government with these actions unless the country pays billions to contribute to Trump’s border wall.

“We have the moral high ground here, and all of the leverage,” Trump wrote. He criticized Mexico for having “taken advantage of us” with drug traffickers and gangs that “committed vast numbers of crimes inside the United States.”

The memo builds on Trump’s previous talking points that he would confiscate remittances sent by illegal immigrants to Mexico to pay for the border wall. Nearly $25 billion was sent to Mexico from migrants living abroad—many of them in the United States, according to the Post. There’s no accurate measure of how much of that total is sent by illegal immigrants.