Donald Trump said early and often that he would get Mexico to pay for a wall on United States’ southern border. Details were to come later. Well, he’s finally explained that he’d do so by stopping wire transfers from illegal immigrants in the States to their home country. It’s a border security policy that contradicts his vow to deport the estimated 11 million illegal immigrants in the United States.

According to a memo to The Washington Post, the Trump campaign said a Trump administration would use the Patriot Act to impound the remittances Mexican expatriates are sending back to Mexico. The Trump campaign claimed $25 billion is being funneled to Mexico each year. “The majority of that amount comes from illegal aliens,” the memo read. “It serves as defacto welfare for poor families in Mexico. There is no significant social safety net provided by the state in Mexico.”

That isn’t quite true, however, as the $25 billion comes from all Mexican expatriates, regardless of country. Though, about 98% of them work in the U.S. This cash represents about 2% of Mexico’s GDP.

As a result of the economic pressure, the Trump campaign expects Mexico will fork over a yet-to-be-determined billions of dollars to build the wall. (In the past, Trump said his plan would cost $8 billion.) If that doesn’t work, a Trump administration will deploy tariffs and cancel visas. “The purpose of Trump’s plan is to punish Mexico for illegal immigration and force it to stop encouraging the border flow,” wrote Ed Morrissey at Hot Air. “Whatever else one thinks of Trump, this plan shows he’s been thinking about the issue more than some would credit.”

But while he tries to use illegal immigrants as leverage for his 1,989-mile wall, his promise to deport all the illegal immigrants undermines that deal. According to a recent report by the American Action Forum, kicking all the illegals out would take $400 billion and 20 years to complete. And no matter what he offers, that’s a deal that neither Mexico nor the American people could pay.