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WASHINGTON — President Donald Trump has repeatedly said he has complete authority to reopen the country for business after the devastating effects of the coronavirus, calling when and how to do so the "toughest" decision of his presidency even as governors and legal scholars contend that he has no such power.

"I'm going to put it very simply: the president of the United States has the authority to do what the president has the authority to do, which is very powerful. The president of the United States calls the shots," Trump said Monday evening, pressed on his claim during a news briefing at the White House.

He asserted that "numerous provisions" of the U.S. Constitution give him the power to potentially overrule governors who have issued stay-at-home orders for their states, telling one reporter that he would provide a "legal brief" to prove it.

He continued: "When somebody’s the president of the U.S., the authority is total, and that’s the way it’s gotta be."

But experts — and the Constitution — say Trump is wrong. The authority to require businesses to close in a public health crisis is what is a known as a "police power," and it is reserved by the Constitution to the states, not to the federal government.

....It is the decision of the President, and for many good reasons. With that being said, the Administration and I are working closely with the Governors, and this will continue. A decision by me, in conjunction with the Governors and input from others, will be made shortly! — Donald J. Trump (@realDonaldTrump) April 13, 2020

The president didn't shutter the country — governors did, using authorities afforded to the states to quarantine and isolate — and he can't simply announce its reopening.

"There's no statutory authority for the president to do that," Stanford University law professor Bernadette Meyler said. "And there's definitely no inherent constitutional authority.

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"The quarantine power is one of the states' oldest powers," she added.

Forty-two states are under state-ordered lockdowns, while three more have partial stay-at-home measures, according to NBC News' tally.

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The president also lacks the authority to direct governors, mayors or other local officials to lift their emergency orders, Meyler said.

While state laws vary widely, most give governors or state public health officials the authority to limit public interactions in emergencies.

Washington state's law, for example, says that the governor "after proclaiming a state of emergency ... may issue an order prohibiting ... any number of persons, as designated by the governor, from assembling or gathering on the public streets, parks, or other open areas of this state, either public or private."

That includes banning such nongovernmental gatherings as sporting events or concerts and closing down businesses or restricting their operations to limit the spread of infectious diseases.

Josh Blackman, a conservative legal expert at South Texas College of Law Houston, said, "I don't know what it means for the president to 'open up the states.'"

"The president does make certain declarations about critical infrastructure and other guidelines that states generally follow. But the president cannot order the governors to do anything. I don't even think he could withhold funding from states, absent a congressional appropriation," Blackman added.

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And while the president has made it clear that he is eager to restart the economy, public health officials and other authorities warn that an immediate return to normal life would likely trigger a surge of infections.

During his daily news briefing Monday, New York Gov. Andrew Cuomo said the reopening process in his state would happen in stages in coordination with other parts of the Northeast — and would be complete only with the advent of a vaccine, which could take as long many as 18 months.

"It's not going to be we flick a switch and everybody comes out of their house and gets out of their car and waves and hugs each other and the economy starts up," Cuomo said.

Appearing on MSNBC later in the day, Cuomo was more blunt.

"The governors had to close the economy, which was not politically easy to do," he said. "But now the federal government can open it? Well, why didn't you close it if you can open it?"

Jane C. Timm reported from New York, and Pete Williams reported from Washington.