“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.