MANPAD means Man Portable Air Defense System.
It is literally defined as something one person can carry. As in, across the border. By yourself.
No air drone surveillance that sees such a weapon walking across? I know the border is bad, and permissive of many things, but didn’t think they were this derelict. But I suppose yeah, it could be smuggled in pieces or like drugs flood the zone, send dozens of them and maybe a a few will get through. But if they found even one, that should have set off all kinds of “red flags”.
Now that I think about it, Eric Holder sent thousands of weapons to the Mexican cartels too….