Presidents have a lot of Constitutional powers: the power to wage war; the power to veto laws; the power to pardon criminals; the power to appoint Supreme Court members and other judges. But President Donald Trump and his inner circle appear to be acting to add a new power to the repertoire, one which would constitute one of the largest expansions of presidential power in modern history: impoundment.

Their theory is that the president has a constitutional authority to withhold, or “impound,” spending from projects after that spending has already been authorized by Congress. Advocates cite examples of past presidents impounding various programs until Congress shut down the practice with 1974’s Impoundment Control Act, which Trump allies view as an unconstitutional law and a congressional power grab.

Trump himself attempted to use impoundment and related powers several times during his first term, most famously to delay paying aid to Ukraine in an attempt to force a prosecution of Joe Biden’s family in that country; this act directly led to Trump’s first impeachment.

Trump’s second term, though, could see a much more extensive use of the power. His nominee to run the Office of Management and Budget (OMB), Russ Vought, was on the front lines fighting for broad impoundment power in the first term, and has sought sweeping cuts to programs like Medicaid and food stamps.

Now in the first days of his new term, Trump is signaling that he intends to push the boundaries on impoundment. On Monday afternoon, news broke that the Trump administration is apparently freezing nearly all federal grants and loans, both domestic and international. That essentially seems to pause what could amount to hundreds of billions of dollars in money appropriated by Congress for specific purposes.

According to a memo released by Matthew Vaeth, acting director at OMB, the temporary pause will come into effect today at 5 pm. By February 10, agencies are required to submit to OMB detailed information on any program or policy affected by the pause. It’s unclear if the money will again begin flowing after that deadline, though if nothing else, it seems the Trump administration is claiming it has the unilateral power to at least temporarily impound billions of dollars.

What happens next on both this temporary pause and any future attempts to impound spending isn’t clear. If, as is likely, Congress tries to resist some of these cuts, Trump and Vought, as well as their flashy spending-cut consultant Elon Musk, could attempt to use impoundment power anyway, sending the fight into courts. There are multiple Supreme Court decisions suggesting such an attempt would be illegal and unconstitutional — but today we have a court where Trump himself appointed a third of the members, and which recently granted him sweeping immunity from prosecution.

If the Court sides with Trump in such a fight, it could set the precedent that presidents can effectively cut spending without Congress, which could have vast, far-reaching implications for everything from health care to defense to science.

Here is what impoundment power is, how it has historically worked, how Trump’s team wants it to work, and why Trump’s view of the power could set the stage for a massive executive power grab, altering fundamentally the relationship between Congress and the president.

Impoundment, explained

The official definition of “impoundment,” per the Government Accountability Office (GAO) that oversees the practice, is “any action or inaction by an officer or employee of the federal government that precludes obligation or expenditure of budget authority.” In other words: any time someone in the federal government doesn’t spend money that Congress has ordered it to spend.

This takes two forms:

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