> wanted to ban travel for people holding PRC passports
Banning by passport makes some sense. We can't prevent US citizens from returning to their homes. But we can prevent others from traveling to the US. It might make sense to ban all passports except the US for flights originating from China, but then you end up dragging in connecting flights through China from other countries. In terms of a quick, easy to implement measure, that will at least reduce the number of imported cases, banning travel based on PRC passports seems logical.
> the disease had spread widely enough that there weren't really many places that should have been whitelisted
Surely, given that we do care about just controlling the numbers even if it is not perfect (like with "flatten the curve"), it makes some sense to focus on the epicenter.
SCOTUS has ruled that the US does have quarantine powers for medical emergencies, even for its own citizens. Maybe a complete ban if poorly orchestrated might run afoul of the Constitution, but a policy like "all travelers [US citizen or not] from X region must present at <specific port of entry>, whereupon they will be transferred to a quarantine facility for 14 days" would totally be fine. Note, for example, the way that the quarantine on dogs because of rabies is being handled.
> But we can prevent others from traveling to the US. It might make sense to ban all passports except the US for flights originating from China, but then you end up dragging in connecting flights through China from other countries.
Why should you exempt people whose only presence was via connecting flights? This generally involves long layovers inside of airports, where a large enough fraction is potentially susceptible to already be concerned about (due to local people making their flights), and you're likely to be spending a decent period of time on the plane with such people as well, too.
Trump wanted to use some inappropriate names for the disease and wanted to ban travel for people holding PRC passports. Neither of those things make sense to do from a disease control standpoint. If you wanted to ban travel for people who had been in the area of exposure, that might make sense, but nation of passport isn't the way; and after not a whole lot of time, the disease had spread widely enough that there weren't really many places that should have been whitelisted.