The same way the USSR lost. People talk about final-point reasons like economic issues caused by an arms race or whatever, but that's just the final steps of a long lost race. Empires collapse long before they finally fall due to inertia alone. And I think the "real" cause is always the same. When enough people inside an empire want it to fail, that empire will fail.
And a common cause for creating that sentiment (that applies to everything from Rome to the USSR to the US) is Empires naturally tend to spend an increasingly disproportionate amount of their time focused on affairs outside their borders rather than within them. You have urban left leaning types becoming increasingly anti-capitalist, and the more right leaning and rural types feeling neglected by both internal and external policy.
People agree on less than ever, but the one thing they all agree on is that the system sucks. This will likely result in over more radical shifts between presidencies. You end up with a country that's starting to feel a lot like a boat being rocked back and forth with increasing vigor. And obviously this isn't just the US. It seems many political systems throughout the world are headed towards dramatic shifts.
Economic issues can cause an empire to start effectively dissolving itself, as happened with the British Empire, but that's not what happened with the USSR. It was forcibly dissolved from within as regions began literally just declaring their independence and refusing to recognize central authority, and that was largely caused by decades of increasing dissatisfaction with the system that simply reached it's final decline under the policies of Gorbachev.
One can also look to examples like the US which survived numerous catastrophic economic collapses, like the Great Depression, wholly intact.
I don't think there needs to be a dichotomy between the two. Leaders of a system tend to come from that system, and are not immune to such discontent, and are themselves even often victims of said systems - which shapes them in the future. Gorbachev lived through Stalinism and his early political positions would include strong advocacy for de-Stalinization. And similarly, if you've never read about Xi Jinping's early life [1] it's extremely enlightening with regards to the nature of his character.
To put this another way, would the USSR have lasted longer if not for Gorbachev? Almost certainly. Would the USSR exist today if not for Gorbachev? That, I very strongly doubt, certainly not in anything like its historic character. It's similar to e.g. slavery in America. Did Lincoln end slavery? Absolutely. Would slavery have ended without Lincoln? Absolutely, and perhaps in an even more desirable fashion.
Pretty much all the "USA #1" types place Peak America after WW2, not before it. Reasonable historians would agree that it was less of a world power than the European nations before WW1, roughly on-par at the time of the Washington Naval Treaty, and surpassing them at some point between 1930 and 1945.
The Great Depression did a lot of damage to individuals but FDR's response to that, and later the war, strengthened the US as a nation.
While I would describe the economic transition of the USA going from laissez-faire to New Deal as being as much of an "end of capitalism"* as the collapse of the USSR was the "end of communism", the country of the USA itself remained cohesive in the New Deal.
As Russia itself was cohesive, I guess you could analogise e.g. Texas to Kazakhstan (leaves), and Alaska to Siberia (remains)?
* as it was understood at the time, and to my limited grasp of the history of such matters
Losing geopolitical influence, respect, and significance. Losing economic impact. Dramatically losing scientists, researchers, innovation, and the things to build future technologies. Losing the lead in electric vehicles and renewable energy. Losing the ability to build ships, semiconductors, large steel foundries, and more essentials.
Given that the original post cites a cold war the US is losing, I'd list these things as part of that war. Russia controls many aspects of the US now, and is bringing about these collapses on purpose. As one does in a war against one's deadly enemy. It's not particularly mysterious.
