It's subscriber-only, but Edward Luttwak's critique of the American declinists is worth your time. Cliff's Notes version:
The future of both the United States and Europe will be shaped by their true strengths - private innovation on one side of the Atlantic, local and regional authenticity on the other - rather than the weaknesses of each that now generate fears of decline. The things that count in the race to the future are human capital, social trust and institutional coherence. The first requires not only excellence and innovation in education, but also openness in learning from others and in absorbing others into our own fold. The second requires balancing that openness with stability and community integration. And the third requires a dynamic combination of resilient federalism and subsidiarity - the shock absorbers needed to navigate safely a fast-paced globalized world. The United States and Europe are in a far better position in regard to all three assets than is any other society on the planet.
For further reading on the myth of American decline, be sure to check out Robert Kagan and Robert J. Lieber.