Donald Trump’s notion of shifting money from the military to pay for his southern border wall appears stalled and likely dead, with congressional sources saying they haven’t heard a thing from the president’s aides.

Senior congressional aides and experts point to several legal hurdles Trump’s out-of-the-blue idea would have to clear. And even if they got over those, Democrats would have to sign off in a midterm election year. Both make the prospects of the president’s idea becoming reality very unlikely, aides and experts say.

What’s more, White House officials have yet to show they are even attempting to pursue Trump’s notion, bucking the president on his latest idea for achieving a major campaign promise that fired up his conservative base and put him in the executive mansion in the first place.

Four congressional panels would have to approve shifting money from the Pentagon to the Department of Homeland Security, which runs the border barrier program. The House and Senate Appropriations and Armed Services committees, which have jurisdiction over Defense Department monies and how they are spent, would have to sign off on such a “reprogramming action.”

Aides for those committees say they haven’t heard anything from the White House about Trump’s idea.

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Such a high-profile transfer of federal dollars would likely take months of discussions among White House, Pentagon and DHS officials, along with lawmakers and senior congressional aides. But four days after Trump floated the idea in a Sunday morning tweet, committee aides have little more than shrugs — and some sarcasm — to offer about the president’s proposal.

“We have no detail on the ‘plan’ at all,” one House GOP aide wrote sardonically in an email.

A Senate Republican aide was more diplomatic, saying the administration has not reached out with any details or requests.

Congressional sources said transferring military funds to DHS would likely require the approval of both chambers — not just the four committees that allocate and oversee Pentagon dollars.

“There is no legal way for DoD to transfer appropriated funds to DHS without new legislation from Congress,” the House GOP aide said.

A Senate Appropriations aide concurred, saying “the committee is not aware of any authority that would allow the DoD to do that without congressional approval.”

That would be an uphill climb for the president because it would require a handful of Senate Democrats to vote with Republicans. Since most Democrats oppose the border wall, such a reprogramming bill would likely die the second it was printed. And with November’s midterm elections approaching, Democrats are not inclined to hand Trump and GOP congressional candidates what would be a huge win.

Then there is Title 18 of the U.S. Code, which states the military cannot be used as a “posse comitatus” unless “expressly authorized by the Constitution or an Act of Congress.” In short, that means the military cannot be used as a police force or for law enforcement functions.

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Securing the U.S.-Mexico border is the job of U.S. Customs and Border Protection and other law enforcement entities. That means “it is highly unlikely that DoD would have any legal authority to conduct the work on their own without congressional sign-off,” the House GOP aide said.

A White House spokesman was asked multiple times this week if the White House had considered the “posse comitatus” issue, but had no response.

The same spokesman did not dispute the notion that the idea is going nowhere when asked about congressional sources reporting no contact from White House or administration officials. Rather than rebut what the sources said, he merely referred to Press Secretary Sarah Huckabee Sanders’ comments Tuesday that she couldn’t “get into the specifics of that at this point,” a line she repeated several times during that day’s briefing.

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Sanders was also asked whether the White House counsel’s office had informed the president that he lacks the legal authority to move the funds himself.

“The president would certainly work with White House counsel to make sure any action he takes is fully within his rights and his executive authority,” she said.

But she never said the White House’s top budget office is preparing a formal reprogramming request to try to make the president’s proposal a reality.

Stan Collender, a former staffer for the House and Senate Budget committees, noted all federal departments have a “very limited” ability to shift funds from program to program.

If lawmakers “are doing their job — not a sure thing these days — the House and Senate will demand that DOD get their permission to do this,” he said. “That should kill any chance that it happens.”