A nation is only as trustworthy as its leader. With Trump as president, that means the US cannot be trusted at all.
A treaty wouldn't have changed anything. Trump would just have told the Kurds "so sue me" the way he & his his minions are defying Congress. He doesn't care and must be made to care.
The strategic strength of democracies and alliances between them is based on institutional continuity. Leaders & parties change, but treaties and goals remain. That strength was decaying long before Trump obliterated it.
