Michael Beckley's article, "China's Century? Why America's Edge Will Endure," provides an interesting framework for discussing this question. He writes that the rise of China is the most read-about news story of the 21st century.
The Global Language Monitor's survey of 50,000 publications worldwide shows that the China ascendancy story has surpassed 9/11 for total world readership.
U.S. "declinists" see the U.S. as turning benefits of the global reserve currency and globalization into economic hegemony which cannot be sustained. These authorities believe either though benevolence or impotence that the U.S. is unable or unwilling to maintain the future international order. These discussions often use the term, "multi polar world" when producing their dire forecasts.
The U.S., according to Beckley, spends 25% more in real dollars than it did in 1968 at the height of the Vietnam War. However, as he rightly points out, the U.S. effectively guarantees the security of some 50 nations worldwide, and those countries, including the wealthy Japanese, get a very valuable free ride.
Turning to historical comparisons, Beckley notes that spending 4% of GDP on defense is not in the realm that has financially undone hegemonists like the Roman Empire, which ultimately overextended itself and its legions with far flung outposts.
Looking at GDP comparisons can be misleading, most of all because that number it itself inadequate as a measure of global political power and the ability to project that power. In a chart, Beckley's article shows that the average Chinese citizen is $17,000 poorer relative to their American counterpart in 2010 compared to 1991.
As a nation, our politicians and Wall Street are in love with numbers. Unfortunately, government numbers are modern propaganda and should be treated with disbelief. Wall Street's numbers are generated by promoters and should be treated wtih skepticism. So, we are told that Chinese GDP has and will continue to grow at 8% per year. That means it doubles every nine years.
This growth has not come in a sustainable model. Beckley points out that much of China's investment has been funneled through investment entities connected to local governments, which issue debt. Taking this local government debt into account, China's debt to GDP ratio goes from the stated 19% to 75-150% .