There is no way the US in anything like its current form can continue for more than a few more decades. The American capitalist class has been forced into a state of hyper-cannibalism by the rise of China and the falling rate of profit. It has lost the capacity for class mediation through any mechanism except violence. The worst case scenario (outside of nuclear apocalypse, which would also destroy the USA) is a period of open fascism, and such a thing can only ever last a few decades. Fascism is inherently unstable and constantly accelerates its own contradictions. The free land and imperial plunder that undergirded fascist-like US colonialism has been squeezed for all its got. This system is absolutely doomed.
Maybe some radically transformed thing called the USA emerges from the ashes, but it would need to be a state with a fundamentally different approach to class mediation that, I think, could emerge only from a dramatic break in continuity and the de facto end of the USA as it has existed to this point.
I haven't read the whole Melenchon piece yet but I do agree that excerpt is not a very strong argument, pretty idealistic.
be the mega you wish to see in the world