This is very hackable.
One simply takes a small plane into the US.
US small airports, and especially private airports don't have YVR level
security.
All in all -- a bureaucratic solution to foreign aid and failed foreign
policy problem.
Not a single terrorist cell will be stopped from forming.
There are plenty of flights going to South America from Africa.
South America can be reached by Pacific Islands using routing that does not
place one into US Pacific Islands Territories airspace.
This policy will take many months to fully implement, and by then the groups
in question will have adapted to the new transport conditions.

Best solution:
Get US birth certificates from children that died -- in order to get US
passports.
The US has no national "Births and Deaths" registry, like Iceland.


Note:
Small planes can land at remote airstrips, and take off with enough reserve
fuel to return to Mexico.
I suspect that Canadian domestic flights will have to be rerouted into
Canadian airspace, a move long overdue.

Yep, the latest antiterror rule from the Bushies will force all airlines
to give passenger lists to Washington for all flights just PASSING OVER
US airspace. That's right, if the flight is NOT going to or from a US
airport, but is merely passing over US airspace, the airline must give a
passenger list to the US govt and it will be checked against the no fly
list. This means that if a flight is going from Vancouver to Montreal,
IOW a Canadian DOMESTIC flight, and the flight passes over US airspace
(something that happens fairly often with Canadian domestic flights),
the Canadian airline will have to check with Homeland Security first to
see that no forbidden passengers are on it.