Originally Posted by
dinoscool3
Well they weren't completely unchecked. They passed through EU security, they passed through EU emigration, and (presumably) their passports and visas were briefly checked by IB check in and/or gate agents. CBP wasn't able to do their checks which, sure, is a problem, but its not like the passengers were completely unvetted and are all criminals and terrorists that are now going to spread throughout America.
Exactly. Any criminal or terrorist worth his salt is going to cross the swiss-cheese southern border completely unchecked, rather than board a flight in MAD where one would fully expect to have to properly clear CBP.