Let's not forget America's strengths. It is the only country that can project military power globally. While China will increasingly challenge its power-projection capabilities in the Asia-Pacific, it is unlikely to rival US military capabilities on a global scale for some time.
The US accounts for roughly a fifth of gross world product, has the world's only reserve currency, maintains a higher-education system that attracts the most international students, and nurtures an entrepreneurial environment that continues to entice many of the world's most creative thinkers.
While America's advantage in these categories may well continue to diminish, the country will remain a linchpin of the global economy.