Lucky geographic positioning during WWII + absorbing the British empire post war

Unless you meant like "How" in the sense of "by what definition" in which case I'd say that being a superpower doesn't really require the domestic situation to be good. Just that your military and influence is dominant in places across the globe

The US is sinking like that Titan submersible... pressure is building, seams are creaking, implosion seems inevitable and imminent. And we're even being piloted to our doom by a narcissistic billionaire. (I should probably save this analogy. Pretty good one)