Constitutional law expert and Harvard professor Lawrence Lessig dismissed President Donald Trump’s characterization of the immigrant situation at the Mexican border as a crisis on Sunday, then said the real national emergency was “this president.”

Asked about Trump’s threat to declare a national emergency on the southern border so that he can order his wall built without congressional approval, Lessig told MSNBC: “The man is using words that have no connection to reality.”

“He says we have a national crisis ... a national emergency. I agree we have a national emergency, but the emergency is this president,” Lessig added. “The emergency is the fact we don’t have an executive who’s exercising his power in a responsible way.”

Lessig said the president can’t build his wall without the backing of Congress.

“Ultimately he has no constitutional authority to exercise the power to build this wall without Congress’ approval,” Lessig said. “These statutes were certainly not written with the intent to give a man like Donald Trump the power that he’s now claiming.”

In an opinion piece Lessig published in The Guardian on Friday, he said the Constitution would not uphold the actions of a president who shut down the government to insist on a program that was not supported by the public. Lessing referred to the situation as a “veto-ocracy,” ruled by “petulance” rather than “principle.”

If the Republicans support Trump in this, they are saying that any president can “support whatever policy he likes,” including, say, to nationalize health insurance.

“The fools are they who enable this constitutional immorality,” Lessig wrote. “Those fools are the Senate Republicans, who have placed party over country, and President Trump over the Republican Party.”