As President Donald Trump continues to escalate his threat to declare a national emergency to construct a wall along the U.S.-Mexico border—and amid reports that his administration is already laying the groundwork for the declaration—legal experts and progressive critics warned against the notion that the move would be a mere political “stunt” and argued it would spark a full-blown constitutional crisis.

“This is a constitutional crisis, plain and simple,” Stephen Miles, director of Win Without War, wrote in a series of tweets on Thursday following Trump’s brief visit to the border, where he said he will “most likely” make good on his threats to declare a national emergency.

“The constitution gives Congress solely the power to appropriate funds,” Miles added. “They have done so and Trump is planning to unilaterally take those funds and use them for another purpose for his own political agenda… If he can claim anything is a crisis to get what he wants, there is no meaningful balance of power.”

While many legal experts have argued that declaring a national emergency to fund the construction of a border wall would be an illegal abuse of power, Miles argued that there is “no reason to believe” the courts—and particularly not the conservative-dominated Supreme Court—will stop Trump from bypassing Congress to construct a border wall that most Americans don’t want.

In a recent piece for the New York Times, Yale law professor Bruce Ackerman argued that not only would Trump’s proposed emergency declaration be illegal, “but if members of the armed forces obeyed his command, they would be committing a federal crime.”

“What this all adds up to is a potential crisis much graver than whatever immigration emergencies the president has in mind: A legally ignorant president forcing our troops to choose between his commands and the rule of law in a petty political struggle over a domestic political question,” Ackerman concluded.

While it is not at all clear when or even if the president will declare a national emergency, Kristen Clarke—president and executive director of the Lawyers’ Committee on Civil Rights Under Law—echoed Miles and others in arguing that the move would spark a constitutional crisis.

“If Trump invokes ’emergency’ powers to build his wall, this would thrust the nation into a constitutional crisis,” Clarke wrote. “No president in the last two centuries has invoked emergency power to fund a policy goal after failing to secure approval from Congress.”

Warnings about the dire implications of Trump’s possible national emergency declaration over a non-existent crisis came as NBC News reported on Thursday that the president is considering a plan to divert billions of dollars away from from disaster relief and prevention efforts in Puerto Rico, Texas, and California to fund the construction of “315 miles of barrier along the U.S.-Mexico border.”

“Under the proposal,” NBC reported, “Trump could dip into the $2.4 billion allocated to projects in California, including flood prevention and protection projects along the Yuba River Basin and the Folsom Dam, as well as the $2.5 billion set aside for reconstruction projects in Puerto Rico, which is still recovering from Hurricane Maria.”

In a statement, Rep. Nydia Velázquez (D-N.Y.) said it “would be beyond appalling for the president to take money from places like Puerto Rico that have suffered enormous catastrophes, costing thousands of American citizens lives, in order to pay for Donald Trump’s foolish, offensive, and hateful wall.”

“Siphoning funding from real disasters to pay for a crisis manufactured by the president is wholly unacceptable and the American people won’t fall for it,” Velázquez added.