This is the purview of the FBI. The NSA is focused on the rest of the world.
Is there overlap? Sure. But the amount of disinformation on the website about the FBI vs the NSA is comical. If anything, when people say “NSA” they really mean “CIA” and just don’t understand the difference.
>The NSA is focused on the rest of the world.
In the same way that the CIA doesn't sell cocaine.
I'm sure they "mostly" focus externally but that doesn't mean they're not still doing a hell of a lot domestically.