I believe showing Russia, China, and the world, that USA stands behinds it commitments and allies, defends the rule based world order and is true leader of the democratic society would deter leaders such as Putin and Xi from trying anything.
NATO is (imo) close to collapsing. All it would take is a minor just-under-war incursion, e.g. in northern Finland by Russia. Would USA (Trump) defend Finland in this scenario? If not, NATO is dead and the next 100 years belong to China and Russia.