FIRST ON FOX: The White House has already started mapping out how to make good on its promise to slash federal spending in preparation for a six-month government funding bill to pass through Congress.

Two people familiar with the conversations told Fox News Digital that President Donald Trump and Office of Management and Budget (OMB) Director Russell Vought are working on a strategy for impounding federal funds that Congress is expected to allocate this week, before the partial government shutdown deadline on March 14.

Trump and his allies have made no secret of their belief that the Impoundment Control Act of 1974 is unconstitutionally constraining the powers of the president. But the new development is a significant step toward a likely legal showdown as Democrats warn they will respond if Trump tries to bypass Congress on federal spending.

The fight could go all the way up to the Supreme Court.

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It comes as Senate Republicans and Democrats are at an impasse over a Trump-backed government funding bill known as a continuing resolution (CR). The Senate GOP needs as many as eight Democrats to cross the aisle and vote for the bill, which the left has widely panned as an avenue to let Trump and Elon Musk dismantle the federal bureaucracy.

The measure is a rough extension of fiscal year (FY) 2024 funding levels, meant to carry the government through the beginning of FY 2026 on Oct. 1. 

It's the third such extension since the beginning of FY 2024, but the first to take place under a fully GOP-controlled Washington. 

Republicans have said it would give them more time to cobble together conservative spending bills for FY 2026, and have celebrated the CR essentially freezing government spending for a year.

Trump and House GOP leaders worked overtime convincing holdouts to vote for the CR this week, as some conservatives balked at the idea of extending Biden administration-era funding.

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But the promise of Trump using Congress' funding allocations as a ceiling and not a floor ultimately played a big part in convincing conservatives.

"We appropriate, that’s an important principle. But then the chief executive can make decisions below that spending level. The chief executive can say, ‘Hey this isn't the best use of money,'" Rep. Chip Roy, R-Texas, told Fox News Digital in an interview this week.

Roy has been a key figure in government spending talks, acting as a liaison between conservative fiscal hawks and leaders in the House and White House.

He and Rep. Ralph Norman, R-S.C., both agreed with Vought and Trump that the Impoundment Control Act – which was passed in response to Congress at the time believing President Richard Nixon was holding back lawful funding because he disagreed with it personally – was unconstitutional.

"The chief executive can say, ‘I don't have to buy a $500 hammer, I can buy a $100 hammer. I don't have to buy a $100 million carrier, I could buy $50 million carrier,' or whatever. He's the executive. So if that money is then spent properly to carry out the functions of government, why should you have to spend every dollar of it, right? It’s literally unconstitutional," Roy said.

Roy said he believed the same authority would apply to a Democratic president.

"By the way, I realize this means that would be true for Joe Biden or that would be true for some future Democrat, and I'm OK with that. There's always going to be some debate," Roy said. "There's going to be some contours the courts would give us. Congress might step in and clarify the law, and that might be deemed constitutional… but to blanket to say the president can’t impound, I think is facially unconstitutional."

Norman told Fox News Digital, "The 1974 impoundment act was against Richard Nixon. It’s a different day now."

He also said Trump and Vought were "going to move forward" on impoundment.

"He’s got the constitutional right to do it, so he’s going to push on with it, and thinks the courts will ultimately side with him," Norman said. "I can't get in Trump’s mind, but I know he’s hell-bent on interpreting the Constitution as his right to use impoundment."

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Rep. Dan Goldman, D-N.Y., who served as House Democrats' lead counsel during Trump's first impeachment, told Fox News Digital the move would be patently unconstitutional.

"It is illegal for the president to act unilaterally and either rescind or change congressionally designated funds," Goldman said.

In the event of likely court challenges – which Goldman pointed out were already going on with Trump moving to cut various programs – House Democrats would likely move to help, he said.

"We can file an amicus brief, and we likely would do that on such a critical issue of congressional power," he said.

At the same time, both Roy and Norman signaled Trump's congressional allies were discussing rescission as another avenue to spend less than the CR allocates.

The Impoundment Control Act provided a mechanism for the legislative and executive branches to enact spending cuts via specific rescissions. Such a bill would only require 51 votes in the Senate rather than the standard 60-vote threshold for passage, meaning Democrats in theory would not be needed.

"I think that they are concurrent plans, and we will use all of those tools at the appropriate time, but I say that as an observer from Congress," Roy said, noting he had no insight into White House discussions on impoundment.

Norman said Musk's Department of Government Efficiency (DOGE) will play a role in identifying where the funds could be found.

"There’s going to be a lot of things in it. What DOGE has done is identify, but now if he’s just going to identify and we don’t move forward on rescission – it’s gotta have some effect," he said.

It's not immediately clear if such conversations have reached House GOP leadership, however. Norman said they were "just beginning."

But lawmakers have been toying with the idea of Trump pursuing spending cuts after the CR is passed for days.

Vice President JD Vance huddled with House Republicans behind closed doors earlier this week, making an 11th hour plea for unity on the looming CR vote.

Among his pitches, people told Fox News Digital at the time, was the need to keep the government open to allow DOGE to do its work.

"We will have much more flexibility for DOGE cuts once we've had more time to identify and quantify them," one House Republican said of Vance's message.

There's also the matter of whether to repeal the Impoundment Control Act – Rep. Andrew Clyde, R-Ga., introduced a bill to do so earlier this year, and it's gathered a significant number of Republican co-sponsors.

But a senior House Republican told Fox News Digital that while it was "on the table," it's not likely that the Senate's 53 Republicans will get enough help from Democrats to reach 60 votes.

Fox News Digital reached out to the White House and OMB for comment, but did not receive a response by press time.