Fusion power simple enough to be cobbled together from post apocalyptic scrap, teleportation tech (F4), Geck 2.0, AIs, cybernetics, panaceus, sierra madre style matter conversion,
The US now has unlimited power, the ability to convert that power into any desired matter, teleportation, space colonization technology, the ability to rehabilitate damaged ecologies in warfare relevant timeframes, forcefields, stealth tech, functioning ABMs, combat robots, energy weapons, memory tranference...
Either the US takes over the world, and everyone else has to suck it up, or the US goes full bore isolationist, as the rest of the world is now extraneous at best, and an annoying distraction at worst.
Robotic servitors become status symbols, then everyday (cue 101 robot memes), the same with AI and cybernetics. I would expect an explosion of US outposts undersea and across the solar system
Communism goes from being a near overwhelming threat to an anachronistic joke nearly overnight.This probably radically alters US involvement in Vietnam, and the middle east. Much of modern us culture and foreign policy was impacted by fears of communism (and the reaction to that) as well as the perceived and actual failures in of US govt in Vietnam and the ME. No Vietnam draft means no hippies, which probably means the cultural revolution in the US never happens, no Disco (thank heaven), and no yuppie reaction to hippies. US culture today is much more late 50's early 60's in influence. For some ideas of how that might look, consider real-world South Korea today.