Donald Trump considered quarantining New York. Can he do that?

Donald Trump announced today (March 28) that he was “giving consideration” to quarantining New York, New Jersey, and Connecticut—or perhaps just parts of those states—in response to the continuing spread of the coronavirus. Tonight he backed off the threat, saying instead he would issue a strong travel advisory that the governors of the three states should implement. Like many tweeted proclamations, Trump didn’t provide a lot of details about his plans, leaving us to speculate.