No, for international flights the airline additionally checks your passport at the gate (at least in the US).

Correct. And they're essentially acting as outward immigration, since the airline's passport records are used to mark the unwanted/foreigners (like me) as departed.

But the system is quite flaky, my arrival/departure record is missing a few departures - and I think that's where CBP want to improve things, possibly so they can more legitimately claim that someone overstayed when their records are incomplete. (And I guess also to spot passport swaps.)

The airline checks passports on the way out as they are required to bring you back if you are denied entry at the destination. They try hard not to pay that cost, so they want to make sure you have a passport, all required visas, haven't been barred from the destination, and so on.

Normally they do not really pay tor that cost either as your return ticket is void after being denied entry. But it is indeed inconvenient for them.

Fair point, but it does presuppose you have a return ticket, which isn't always the case.

It should come as no surprise the CBP will cooperate with other government departments, i.e. ICE. What would be interesting is finding out how they got funding for this rubbish.

Judging from when they had these at SecTac in June, it just made everything much, much slower.

> It should come as no surprise the CBP will cooperate with other government departments, i.e. ICE

Considering the "C" in both agency acronyms stands for the same thing, it would be more surprising if they didn't work very closely together. Personally, I'm surprised they're separate agencies in the first place.

To make sure you can get into the country when they land. They don't want to fly you back.

They also scan boarding passes at the gate to verify that all checked bags have a corresponding passenger on the aircraft.

Plus they are required to know how many souls they have on board and who.