Except that China cannot keep up the necessary GDP growth to subdue internal unrest.
When the US spends over a trillion dollars each year on defense, it is easy to over-estimate the financial doom. Imagine cutting defense spending in half, still out pacing everyone else in the world's defense spending by at least ten, and having over half a trillion dollars to reinvest in our own economy.
If we keep following the Nixon-Reagan-Bush-Clinton-Bush and quite possible Obama policy toward the military industrial complex, then, yes, we are probably doomed (though Russia is more likely to be the ascendant power). However, if we can manage to elect officials who will heed the advice of Presidents from Washington to Eisenhower, the US will be able to easily avoid this often predicted disaster.