ICE’s scope isn’t who is coming into the country — that’s CBP’s scope. ICE’s scope is supposed to be those committing immigration offences who have already entered the country (either because the CBP failed to catch them, or because they were admitted but never left).

The only difficulty justifying this is ICE’s power to stop and question people, and an airport is no different to a random street from that point of view. Do they have probable cause? What suffices as probable cause?

And once you have probable cause, you run into the problem 8 USC 1304(e) creates: someone who doesn’t have documentation proving their legal immigration status falls into one of two categories, they’re either a citizen, or they’re an immigrant violating that section.

(And this is looking at it from a simple legalistic point of view, ignoring any questions about ICE’s behaviour or powers!)