In concept, to facilitate tracking entries and exits, one is supposed to enter and leave a country using the same document. Years ago, Congress demanded immigration exit controls - something the US has not made much progress on. Effectively, therefore, the US does not have exit controls and commercial carriers pretty much only had to check that the pax had the appropriate documents for the destination. Perhaps this is a new step towards actual exit controls?

It is much easier to implement these things on commercial carriers, and in particular, air carriers, than other forms of travel. Commercial carriers have much to gain by partnering with government...