Yes, he can restrict travel — between states, not within states — of people reasonably expected to have COVID-19.
On Saturday, President Trump announced via Twitter that he may decide to order a quarantine. As he put it: “I am giving consideration to a QUARANTINE of developing ‘hot spots’, New York, New Jersey, and Connecticut. A decision will be made, one way or another, shortly.”
The powers of the federal government in general, and of the president in particular, to quarantine American citizens is not cut-and-dried.
The Supreme Court has long recognized that citizens of the United States have a constitutional right to travel from state to state. In its 1998 decision in Saenz v. Roe (quoting from a concurring opinion by Justice Potter Stewart in Shapiro v. Thompson (1969)), the Court opined that this “right is so important that it is ‘assertable against private interference as well as governmental action . . . a virtually unconditional personal right, guaranteed by the Constitution to us all.’”
This is rather a grandiose pronouncement given that there is no explicit right to travel in the Constitution. Indeed, the word travel does not appear in the document at all. Nonetheless, it was explicitly spelled out in the Articles of Confederation (Article IV states, in pertinent part, “the people of each state shall have free ingress and regress to and from any other state”). The Court has presumed (as the justices reaffirmed in Saenz) that
the nature of our Federal Union and our constitutional concepts of personal liberty unite to require that all citizens be free to travel throughout the length and breadth of our land uninhibited by statutes, rules, or regulations which unreasonably burden or restrict this movement.
This right to interstate travel has three components: (a) the right of a citizen of one state to enter and leave another state, (b) the right to be treated as a welcome visitor while in another state, and (c) the right to resettle in a new state and be treated equally with the citizens thereof.
Of course, no right is absolute, even one said to be “virtually unconditional.” Congress, not the president, has the power to regulate interstate commerce. A federally imposed regulation on the right to travel between states may be upheld, even if the effect is to abide unequal treatment of citizens, if it is “shown to be necessary to promote a compelling governmental interest.” (I’m again quoting Saenz, which quoted Shapiro.)
Obviously, the government has a compelling interest in preventing the spread of communicable diseases. As the CDC explains, Congress has delegated power to the executive branch, specifically to the Secretary of Health and Human Services, “to take measures to prevent the entry and spread of communicable diseases from foreign countries into the United States and between states.” (Emphasis added.) Congress allows the HHS Secretary to authorize the surgeon general to make regulations designed to prevent the spread of communicable diseases from one state to another. Thus have regulations been promulgated permitting the apprehension, examination, and detention of persons reasonably believed to be infected with a communicable disease who are either moving from state to state, or who could be a source infecting others who will move from state to state.
The latter of those two is clearly, at best, the outer margin of federal authority. In our constitutional system, the states are sovereign over internal affairs, including intrastate travel. Even the CDC concedes that it is the states that have the authority to “enforce isolation and quarantine within their borders” — which deftly sidesteps the question of whether the federal government may order an intrastate quarantine that the state must then enforce.
To summarize, although American citizens have what has been interpreted to be a fundamental right to travel between states, the federal government’s very limited power to curb such travel undoubtedly includes authority to prevent the spread of infectious diseases — and COVID-19 certainly qualifies as one. Congress has the power to regulate interstate travel, and it has delegated that power to the executive branch for the purpose of protecting against the spread of infectious diseases.
Consequently, the president does have the power to restrict travel between the states of persons reasonably believed to be infected with COVID-19. I would assume that this means the power to prevent people who reside (or who have recently been present in) “hot spot” areas from traveling from those areas to other states. If that is what President Trump means by “QUARANTINE,” he’s probably on solid ground.
On the other hand, if he is declaring the power to order quarantines within states (meaning, to restrict intrastate travel), that is a more dubious proposition. I would assume that, because the administration has been working effectively with the governors, especially the governors of the states most affected (so far) by COVID-19, the president will make sure to get buy-in from any affected states before issuing an order restricting travel. This is why, so far, he has limited himself to issuing non-enforceable guidance and has not attempted to mandate quarantines.