I think that in many ways, this describes majority of the ins and outs of U.S. politics. There is a tension between different ideological groups trying to acquire power and in order to accomplish their goals and usher in their vision of a better society, they need to toughen up and act with unabashed cruelty to uproot the weak.
And most often, these goals are noteworthy aspirations. I think that to uphold family values, to provide a better means of living for the working class, to ensure the rights of the marginalized, to ensure national security, and etc. are agendas that we should try to accomplish. Generally, though, they require either overpowering opposing views, which can lead zero-sum political battles. Worse, the quest for power to achieve the good can turn one into a monster as noted by Nietzsche:
“He who fights with monsters should be careful lest he thereby become a monster. And if thou gaze long into an abyss, the abyss will also gaze into thee.”
But even if Nietzsche predicts that our human nature will surface, lay to ruins our goodwill, and reveal our brutal reflection, I think that the phenomenon of an American decline can be seen as the progress of change. And difficulties are often the symptoms before change can occur. Hopefully, the struggle for power between conflicting ideologies might end up producing a refined synthesized idea, as Hegel noted before.
But going back to your points, I think that, yes, cruelty and the hunger for power are surfacing more and more in the face of American life and politics. I actually subscribe to this worldview. But I think, as you said, humans are not as simple as Nietzsche had hoped, and we might surprise ourselves in the end and create a much better society — one can hope.