Re: How will America handle being number 2?
Define #1.
In 1990 Japan's economy was bigger than the USA's in outright terms, desite a mere half the population. So what went wrong there? Obviously some large bubbles that when popped caused wrong spending decisions. China could suffer that fate. In spite of almost 20 years of little growth, Japan is still #2 by overall economic size.
Indeed Japan's per capita GDP is over $40,000 a year, China's is $4500. The USA's approaching $50,000. So in truth even if China overtakes the USA in 20 years' time, it also has 5 times the population - and the average Chinese in 20 years time will still have less than half the income of the average American today.
Of course, per capita many countries are ahead of the USA. Generally small populations, benefitting from status as tax havens, from banking, or from natural resources - primarily petroleum and natural gas.