President Donald Trump is still trying to build that wall—yes, the wall that would divide the U.S. from Mexico. And who does he think will fund it? Well, the military, of course.

Trump has spoken privately with advisers about funding the border’s construction using the U.S. military budget, according to CNN. Trump discussed the idea with House Speaker Paul Ryan, while reviewing the omnibus spending bill, which doesn’t include funding for building the wall.

Trump promised the wall would be built during his presidential campaign, even calling for Mexico to fund the project. Of course the country refused, so Trump said he would receive payment through a refund, reimbursement, trade negotiations, or remittance payments.

If Trump was to really pursue funding through the military budget, then he would need to get congressional approval, which isn’t probable. A senior administration official verified that the president had thought the idea over, adding, “There's a lot of different options we're trying to contemplate. Certainly that's one.”

Trump has other ideas up his sleeve, too. An alternative is increasing border fees from Mexico into the U.S. “You could always increase them and take the revenue for that for resources,” the same official said, who also described these options as Trump’s “musings.”

On Sunday, Trump tweeted about the wall, writing, “Because of the $700 & $716 Billion Dollars gotten to rebuild our Military, many jobs are created and our Military is again rich. Building a great Border Wall, with drugs (poison) and enemy combatants pouring into our Country, is all about National Defense. Build WALL through M!”

While at the time, it was unclear what he meant by “M,” the Washington Post published a new report, clarifying the tweet. According to two advisers, the “M” refers to the military. The Post also reported that three people who are knowledgeable about Trump’s meeting with Ryan observed that he barely reacted to Trump’s idea of the military backing construction of the wall. The publication also reported that Trump was "spurned" last week when lawmakers dedicated $1.6 billion to the border wall, well short of the $25 billion he wanted.