Remember that geography (and our completely dominant Navy) means our power is free to deploy worldwide while China is hemmed in by hostile or potentially hostile neighbors. It's the Expeditionary Kingdom versus the Trapped in the Middle Kingdom.
This article goes into why our power will remain dominant in the western Pacific. As a distant power reliant on allies in Asia to project our power to Asia, we are a safer dominant power than China--or anyone else--can be:
This interdependent relationship means that the US is not so powerful that it can readily ignore the wishes of key states, and it is here that its apparent weakness is actually strength. America is not a Hobbesian Leviathan with absolute authority and power. Indeed, China's strategists are frequently puzzled by the lack of "balancing" that takes place against the US in the region. But it is puzzling only if we characterize Asia as being multi-polar rather than hierarchical.
In fact, any balancing tends to take place in order to preserve the hierarchy, not to replace or supersede it. Other states tend to resist bids by any Asian power -- be it Japan, China or India -- to rise to the top of the pyramid. As a foreign-based power, the US needs the cooperation of Asian partners. This keeps the top dog in check. Were an Asian country like China to rise to the top, it would not need the same level of regional cooperation and acquiescence to maintain its position and military footholds.
As China and India rise, and Japan becomes more "normal," they will balance each other within the US-led hierarchy to ensure that the US remains on top and one or the other doesn't dominate. If China makes a bid for regional hegemony, it will find it difficult to resist the structural constraints placed on it within this hierarchy.
Indeed, the rise of Asian powers with offensive military capabilities should increase our influence.
As long as Asian powers were basically large masses of territory and people difficult to conquer from sheer size, but lacking offensive power, Asian powers didn't need to fear each other nearly as much.
But with Asian powers gaining the offensive conventional military power to threaten each other, they may need the help of another power. And as I noted in the post linked above, we retain the greatest amount of uncommitted and deployable military power on the planet.
Don't write off America so quickly. We'll be the power to reckon with for a very long time--unless we screw it up ourselves, of course.
