What crisis in future will lead to downfall of America ?usa survived world war,recession,Chinese threat?

Is usa the last superpower on earth ?whats the crux of Americas progress,is it hardwork determination and the total freedom for people to what they want in America: is everything still same or whats going wrong ? will usa will remain top on next Olympics (total medals ) your thoughts please ? Whats gonna happen in year 2020 will India rise or is it China or apocalypse