The US was running up debts with post-WWII behavior for quite a while, especially with wars in Korea and Vietnam. This is what Charles de Gaulle was talking about when he referred to the US' "exorbitant privilege" in 1965 (https://en.wikipedia.org/wiki/Exorbitant_privilege) before repatriating France's gold. Multiple presidents preceeded Nixon and continued promoting expansionist policy and meddling in foreign countries with war (that the US could not afford if not for our exorbitant privilege), mostly to compete with or try asserting dominance over USSR.