Why do people talk about the decline of American power? Where is the evidence?

[Booh!]

To be honest rumors about the decline of America started with the fall of the USSR in the early 90's. Before that, many countries feared so much the USSR (or the USA, on the other side) that they decided to blindly follow one or the other superpower. As the threat posed by the USSR disappeared many countries began to follow their own agendas and so even the USA lost a lot of foreign support in favor of smaller regional powers.
That was critical for the american economy, in the past the US kept alive their economy imposing their own will: in the early 70's they imposed the OPEC to sell oil in dollars (forcing other countries to buy dollars to buy oil, that is to buy the american debt), in the 80's they forced Japan to revaluate its currency to limit the American trade deficit (causing the greatest economic crisis of Japan).
Today there's no one willing to please the US at its own expense, China refused multiple times to revaluate its currency like Japan did and the American trade deficit is widening, while Iran chose to sell oil in euros. People talk about the decline of American power because they don't see an easy way-out to the current economic crisis.