While the president of the United States is often referred to as the most powerful leader on earth, there are limits to those powers, and one of them is that he cannot order Americans to leave their homes and go to work.
Such a declaration, in the midst of a health crisis, would have to come from local authorities — in state capitals or even from city or county governments.
This longstanding legal principle predates the Constitution, experts say, so Mr. Trump can suggest what counties may go back to work as he did in his announcement on Thursday, but he does not have the authority to overturn state and local decrees.
“States are understood to have a general power to legislate for the health, welfare, safety and morals for the people of their state,” said Andrew Kent, who teaches constitutional law at Fordham University’s School of Law.
There might be some exceptions, Mr. Kent and others noted, as in the case of a military invasion or other national emergency, but a pandemic is not one of them. On health matters, the federal government’s powers are limited to trying to prevent the spread of contagious diseases into the United States or between states.
That formula, giving each state control over the “health, welfare, safety and morals” of its residents is woven into countless legal precedents.
An 1873 Supreme Court decision, for example, upheld the right of Louisiana to shut down a private slaughterhouse on the Mississippi River north of New Orleans to control cholera outbreaks.
Mr. Trump could try to use his considerable levers of power like withholding federal aid, as he did with the sanctuary cities that opposed his immigration policies, legal experts said, but states could reject any direct attempt to interfere in their shelter-at-home orders.
“He has no power to go directly into a state and to tell a business operating in that state that it has to open or change its operations in any way,” said Lawrence O. Gostin, a professor at Georgetown University Law School who specializes in public health law.