In your own words,
When the last superpower on the planet, with no meaningful domestic political opposition, can't successfully carry out "diplomacy, politics, and economics" anywhere, and is also incapable of successfully occupying a totally defeated and helpless nation, is it so unreasonable to conclude that its leadership is just spectacularly incompetent?
I am having trouble trying to come up with a historical example of another nation with so much going for it that was so consistently inept.