Despite all the confusion over the impact of his sudden move Tuesday, the Constitution, federal law and court decisions make it clear, experts tell ABC News: President Donald Trump’s controversial executive order to indefinitely pause federal funding is illegal.

“The basic idea is the power of the purse is given by Article I to Congress,” Michael Dorf, constitutional law professor at Cornell University Law School, told ABC News. “If Congress says you’re spending that much money on the federal programs, that’s how much is being spent. The president cannot stop it even temporarily.”

While past presidents have tried to impound — or hold back — federal funding in specific cases, Trump’s directive to indefinitely freeze financial assistance, grants and loans and foreign aid has taken it to a new level, according to Steve Vladeck, a professor of law at Georgetown Law School.

Despite Trump’s influence and GOP backing of most of his policies, the experts warned that his orders have no legal ground to stand on — and history has shown that such blatant disregard for legislative power has been consistently overruled.

“It’s a question of when, not if, this block is overturned by the courts,” Vladeck told ABC News.

The use of executive power to curtail federal spending came to the U.S. Supreme Court in the 1970s when President Richard Nixon ordered the Environmental Protection Agency not to dole out funding for various programs, including water treatment. The Supreme Court ruled in 1975 in Train v. City of New York that the president had no power to overrule Congress by impounding funding.

Dorf said the controversy over the move led Congress in 1974 to pass the Impoundment Control Act that closed some loopholes and made it harder for a president to try to stop spending money lawmakers allocated.

“Congress passed this statue this very particular rules of what exactly the president has to do if he wants to not spend money on money Congress has spent,” Dorf explained. “He can ask Congress to for a recission, but there is a 45-day clock and a bunch of procedures, none of which have been followed by Trump.”

Trump’s decree, which ordered all funding to pause at 5 p.m. Tuesday, cited vague reasoning for the indefinite halt claiming the White House Office of Management and Budget wanted to review funding that contradicted the president’s previous executive order and “advanced Marxist equity, transgenderism and green new deal social engineering policies.”

The order was done at the behalf of the acting head of the OMB.

Several challenges to the act and executive impoundment have come through the courts, including the 1998 Supreme Court case Clinton v. City of New York that challenged President Clinton’s use of a line-item veto to cut funding, the courts have ruled against executive impoundments.

Vladeck said the broad and vague conditions used to “shut off the entire tap,” violate those precedents and legal language set by the courts.

“They’re likely to make a case that this is not an impoundment because it is temporary,” Vladeck said of Trump’s legal team. “However, the Impoundment Act strictly forbids even a short stop in funding.”

The experts said Trump’s actions were telegraphed by the right wing think tank Project 2025 which proposed using a similar funding tactic, but they questioned whether those proposals were thought through legally.

“During the first Trump administration they botched a bunch of things if they got better lawyers, such adding citizenship question to the census or ending DACA, Dorf said. “It may be that lawyers may not have been consulted and whoever in the budget office decided to say, ‘Do what you can and see what you can get away with.'”

The experts said they were confident that the courts would issue an injunction soon and fast based on the number of legal cases filed against the order on Tuesday.

Vladeck said he wouldn’t be surprised if the order went to the Supreme Court and was confident that the court would overrule the president.

He noted that last May, the court ruled 7-2 in a case that upheld the Consumer Financial Protection Bureau and how Congress decided to fund the agency, despite huge support from conservatives looking to defund the agency.

“I know folks are pretty locked in their views of the Supreme Court but I do not expect this to be a case that divides the justices down the middle,” he said.

Vladeck did warn that while this case is being worked out in the courts, millions of people will be at risk due to the limbo by the uncertainty left by the order.

Many organizations, non-profits and local governments have no idea if they’ve lost federal funding for key programs such as school meals, Medicaid and that confusion has been trickling down ot the public, he said. Even if the funding is restored soon, the public has already taken a hit, according to Vladeck.

“On a scale from 1 to 10, this is a 13. This is not just about the money,” he said.