WASHINGTON — Still angry about the budget deal he signed last week, President Trump has floated the idea of using the military’s budget to pay for his long-promised border wall with Mexico, despite the fact that such spending would likely require approval from Congress.

Trump raised the funding plan with House Speaker Paul Ryan at a meeting at the White House last Wednesday, according to a person familiar with the discussion who spoke on condition of anonymity.

And he’s publicly tweeted that building “a great Border Wall” is “all about National Defense,” and called to “Build WALL through M!”, meaning the military.

Departments, however, have limited authority to reprogram funds without congressional approval. Pentagon spokesman Chris Sherwood referred all questions on the wall to the White House, where spokeswoman Sarah Huckabee Sanders deflected them, saying she was “not going to get into the specifics of that.”

Trump threw Washington into a tizzy on Friday when he threatened to veto the omnibus spending bill, in part because it didn’t include the $25 billion he’d tried to secure for the wall in a last-minute bargaining spree.

The $1.3 trillion funding package did include $1.6 billion in border wall spending. But much of that money can only be used to repair existing segments, not build new sections. Congress also put restrictions on the types of barriers that can be built.

Trump has tried to justify signing the deal by pointing to the boost in funding it provides for the military. But he nonetheless remains frustrated, according to people familiar with his thinking, who spoke on condition of anonymity.

Trump first publicly floated the idea of having the Pentagon pay for the rest of construction in an obscure tweet that left many confused.

“Building a great Border Wall, with drugs (poison) and enemy combatants pouring into our Country, is all about National Defense,” he wrote Sunday. “Build WALL through M!”

He retweeted his message again Monday night.

Some people close to the president have also suggested creating a GoFundMe campaign that Trump could use to raise money from the public to fund construction.