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".
If the country’s “core interests” can be defined and redefined based on the whimsy and preference of the current administration, then for the Trump administration to suggest that a certain thing will “always” be in the core interests of the country is ridiculous. The next administration will have their own core interests. Also, what a waste of resources that is.
> The next administration will have their own core interests.
This is sort of the whole point of elections. The government's core interests are not static. When the article says "always", it's from the frame of reference of the current administration, and it's pretty standard for whoever is the current administration to speak as if their stance has always been correct and will always be correct.
The framing here is that "America" always holds these things to be true, and any past discrepancy from that was due to bad leadership. This writing style isn't unique to today's administration, you can find examples from basically any government across history.
I don't remember that being part of the Constitution.