Serious question—how in the hell are they enforcing this? Because from my experience, they aren't.

Case in point: arrived at IAD today, cleared via GE as normal, and was never asked about my travel history to China in the last 14 days, either by the GE kiosk or by any airport or CBP personnel. Not even a temperature scanner like often seen at airports in Asia. Absent perhaps a direct Mainland China - US flight (or maybe single ticket Mainland China - XXX - US itinerary), it seems like nothing at all is being enforced. Does CBP/CDC not realize that people can fly China-EU-US itineraries (or infinite other permutations) on multiple tickets?

Or—shock—perhaps this really is just more theatre?