Lawrence Kaplan has a nice short piece in TNR that speaks to the debate between John Quiggin and I regarding America's power. There are lots of quotable bits, but you should read the whole thing so I'll only offer one:
Regardless of his own inclinations, President Obama has been presented with successive crises to which he has been obliged, kicking and screaming, to respond. The United Nations has not been able to. Europe has not been able to. Either the United States will respond, or no one will.