I doubts he'll run. He's making too much money, enjoying too much positive press and doing too much good for his cause to muck it up by becoming president. Its not to say that he couldn't do more as president, but his global warming cause would be side tracked by Iraq, health care, immigration, etc.
I think the last thing China would want to do is call America up on its debt. China's economic boom is dependent on America. What do you think would happen if American businesses decided to move to India? The Chinese economy would come to a halt. There is no shortage of cheap labor in the world, but its only in America do you find such rampant consumerism. I also believe that the last thing any nation would try to do is invade American soil. Our nuclear arsenal guarantees security. Last point on the Chinese nuclear class aircraft carriers - I'll concede that they certainly have the man power military advantage over us, but keep in mind when it comes to military innovations, America is in a class of its own. We spend more on our defense than most countries' GDP. The technology that China is using was probably American. I'll concede that China certainly has leverage over the USA, but its been sensationalized.