Empire in decline?
I seem to remember the same being said in the 80s when it was Japan that had the huge trade advantage over the US. Now granted China is FAR larger and will easily overtake the US as world's largest economy without its per capita GDP needing to exceed 30% of the US's, but like Japan did with its aging population China has some demographic challenges awaiting it when the parents of the two "one child" generations reach retirement age, which is just beginning.
The US will never be as dominant as it was in the decades after WW II, but that was a one shot deal mainly because it had the only large industrial base that hadn't been blown to smithereens by the end of the war.