The theory goes like this: America (as the United States, not as the continent) has peaked. We've exhausted our better instincts, and are losing our imperial hubris. The end of Pax Americana is upon us, and this is an end brought about by an inability or an unwillingness on behalf of the United States to be competent. This explains the long-lasting dead-end wars, the bold statements about power that are only followed by fails to properly use that power (see: the War on Drugs, or either of the major wars that have been going on for over 5 years now). The US of today may care about clinging to power, but that's a holding action; we are in decline and the best we can do is put off that decline or go out in a blaze of glory. (No one really considers the blaze of glory a real option, but that is what a war with Iran would be.) The gradual decline is more like what we see happening to New Orleans: a lack of interest, and a feeble attempt to restore horrible prior conditions. Either way, the US is through.
This isn't a line of reasoning I agree with, but I'll run with it. If we take the US's decline as a given, we have a short list of facts to work with:
- The United States is still the most powerful nation on earth at the moment
- That power is not going to dry up for at least a decade or two
- There are several nations who could make a stab at being successors to the US, but none of them are a given
- Given that several nations are capable of succeeding the US, odds are that none of them will make it entirely, leaving several competing major powers but no single dominant power
- Unlike the collapse of every prior hegemonic imperial period (Rome, The Hapsburgs in the 16th century, Imperial Japan, the Tang Dynasty, Great Britain), significant international organizations founded on the rule of law exist
That was a gentle way down for the US. It was a potential hegemon, a nation on the rise, and a nation that could remain a strong ally of the US. But the transferral of hegemonic status is a game that never ends well.
The better way down, the easier option to prevent another nation reaching hegemonic heights, is to make the UN supreme. Not supreme as in a "world government" sort of a way, but supreme as in the ultimate legitimizer and protector of national sovereignty. In a world where every nation fears being powerless to act against a single superpower, the answer is to collectively enable an international democratic body to prevent such a status. The gentle way down is a UN in charge of the global commons.
This position is hindered by the past 4 US presidencies. International law needs to be accepted as ultimately more important than national self interest, and international law cannot be so willfully and fragrantly violated as it has been under the later Clinton administration and under the second and third Bush administrations. The US acting as it did was incredibly short-sighted, and it ruined the chances the US would have at a peak transfer of status. But the potential for such a move still exists, and with luck the next US president will see the unsustainability of current US postions and vouch for a greater empowerment of the UN. It's not the only way down, and it's not the most glorious end to an era of power and prestige, but it is the gentle way down. That, above all else, should be a good thing.