The UCLA states uncategorically that no US citizen can be denied re-entry.
US officials notified passengers aboard the Diamond Princess that they would be denied re-entry "until you are no longer at risk of spreading infection during travel." It becomes even more problematic by stating that the person will be turned away at any boarder (Mexico, Canada, and any sea port) if they have already traveled to the boarder. I question the legality of this action. I understand the US can legally quarantine people, which seems like a legal and rational approach to the issue, but I am not sure if they can banish people like this.