I'm convinced the US needs an existential threat to be successful. Our history is one of ineptitude and international meddling (to put it nicely). We need a USSR or something like it to keep us focused on our own shit.
Pretty sure we already do. The new "axis of evil" is Russia, militant Islamic states like Iran, NK (to the extent they matter at all... they won't, until they suddenly do, I think), and bringing up the rear being the most dangerous of all, China.
Well good news: the PRC (China) will be the needed existential threat within 10 years.