From Part 7 of the US Foreign Affairs Manual:
A child born in an immigration detention center physically
the United States is considered to have been born in the United States
and be subject to its jurisdiction. This is so even if the child’s parents
have not been legally admitted to the United States and, for
immigration purposes, may be viewed
as not being in the United
So you can be in the United States but arguably not IN the United States. You know– in it, but not IN it.