(Please note this is not my point of view, just one I think needs to be added to the debate.)

Some in the left (both from inside the US and outside) look at the foreign policy actions of administrations from both parties over the years and conclude that whilst Bush's cabal has taken things further than usual, it is not the sea change sometimes presented.

That is to say, there is something in the US system of government that lends itself to foreign adventures and something in the US doctrines (CFR perhaps?) that crosses both parties and lends itself to interventions careless of human rights of people on the ground.

Some take this thesis and run with it all the way to "there's no difference between Democrats and Republicans."

Just to emphasise again that I don't believe this, but I do think it's not a completely irrational point of view in the milder form. I'd sum up the critique this way:

The US is (at least in the theory) a country whose internal political system is quite a model of democracy and justice that has lessons for most of the world.

BUT, many people confuse that with an instant legitimacy in the foreign policy arena. The facts of US actions in many parts of the world are that they have involved a goodly amount of anti-democratic, violent, anti-human rights behaviour. This record spans administrations to some degree. Thus we have to conclude that whatever the internal goodness of the US, its system of government does not make it instantly a "hyperpower who should always be acceded to."