It's not. What you quote doesn't claim that it is, either.
The federal government has (at least in theory) limitations imposed by the Constitution. Within those limitations, though, it can operate on any theory of foreign policy that it wants, including that of "core interests".
The federal government has (at least in theory) limitations imposed by the Constitution. Within those limitations, though, it can operate on any theory of foreign policy that it wants, including that of "core interests".