No such guarantee would be meaningful if the US administration and congress change their opinion. Whatever they write in law or sign, they can undo -- if not legally then in practice.

- The US had given security guarantees to the Ukraine when the Ukraine surrendered their nuclear weapons, and then failed to follow them.
- The US had made a deal with Gaddafi to make him drop his WMD programs and then supported his overthrow.
- For that matter, the US had made a deal with Iran on nuclear issues and it is generally understood that Iran held *that* promise, yet the US broke the deal.

The only way for another country to be safe would be to join *another* strong alliance, or to retain sufficient military leverage to make an US attack unlikely.

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On the other hand, US foreign policy doesn't *have* to "change drastically" when the administration changes. Johnson and Nixon both fought the Vietnam war, Bush and Obama fought the Iraq counterinsurgency, and so on.