I first want to say thanks to the OP for posting this article. I'm a big fan of Foreign Affairs and the Economist. I read them whenever I can, but too poor to subscribe to them.
First, I want to say I agree with almost everything the article have mentioned. It's true. Throughout the past 50 years, there have been many naysayers predicting the demise of the US, but as we all know, the US maintained its superpower status during the crises of the past 60 years. The US will remain and continue to be a world power for years to come.
All this talk about China's gain is America's lost is absolutely false. This isn't necessarily a zero-sum game. While I do agree that China will eventually have the world's biggest economy by the middle of this century, it won't be something the Chinese will have for long. Let's not forget that of all the major industralized countries, the US is the only country with a healthy birthrate. Combine that with massive immigration, the US population will probably reach 1 billion by the end of this century. The US will certain be competing with both China and India for economic supremacy long before this century is over.
Make no mistake, Chinese military power is growing with each subsequent year, but it will be checked by US as well as Indian power. India is certainly no friend of China. As long as those two countries have territorial disputes, the US will continue to try its best to engage India in dialogue to surround the PRC. It would be foolish for anyone to assume that China will dominate the world in the near future. They won't as long as they have India and the US suspicious of its intentions.