This week, Larry Summers noticed that countries (including key US allies) ignored the US demand not to join a Chinese economic institution and concluded that the US is no longer the world's economic leader. The East is gradually usurping it.
With Congress seeking to undermine the efforts of the international community to do a deal with Iran on its nuclear capabilities, folks are increasingly going to disregard the US on foreign policy as well.
It's sad to see. The world is better off with a US which understands that to lead you cannot also be self-centred and dysfunctional. But that you gain a lot more than you lose by being the leader. This is an era of mostly rather weak and contrastingly megalomaniac leadership in the senate and house.
Without folks changing the way they operate, I guess this is how the era of US preeminence ends. These right wing Republicans are too extreme and too disloyal to make the world want to to do the US' bidding.