It's abundantly clear that governors and mayors, not the federal government, have the broadest quarantine and isolation authority. That's because the constitution leaves that kind of police power in the hands of the states.

Longstanding federal laws, and rules put in place at the end of the Obama administration, give the Centers for Disease Control and Prevention authority to quarantine people to stop disease outbreaks. The beefed-up rules were imposed after the experience of the outbreaks of Ebola and MERS six years ago.

Broadly speaking, the CDC has the power to detain people suspected of having a communicable disease, without getting approval from state and local officials. It comes under the public health laws that allow the federal government to impose restrictions either on people coming into the country or traveling from one state to another.

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However, that authority is rarely used, and when it has been invoked, it was directed at individuals and small groups.

So could it be used to impose a national quarantine?

Experts on public health law say maybe, but an attempt to do so would likely be challenged in court.

For one thing, the federal authority is limited to restricting the movement of anyone who "is reasonably believed to be infected with a quarantinable communicable disease." It's not at all certain how that would apply to large groups of people. Under the law, there is no explicit statutory authority for a blanket federal interstate quarantine, only for the isolation of individual people deemed infected.

Professor Michael Ulrich, an expert on public health law at Boston University, says any effort to apply that authority on a large scale would lead to claims that the government was exceeding its power. "You have to be able to justify that some group is a credible threat to others, and that's an easier thing to do on an individual level." He knows of no federal effort to do so for a large group.

If someone in the group sued, the government would have to demonstrate why people in an entire region were a threat to carry the disease across state lines. "That's a really hard thing to prove," Ulrich says. Even so, he said, a federal court might be reluctant to second-guess public health authorities and would instead defer to such an order in the face of a national crisis.

During the Ebola crisis, a nurse who returned to the U.S. after treating Ebola victims in West Africa successfully challenged a quarantine in court, arguing it was not medically and scientifically necessary. But the pressure would be much greater on the courts now with so many restrictions already in place.