Just because revolutions are class wars doesn't mean the work like a typical war, most of the time. You won't see factory unions leading tank battles against the 2nd armor division. The American Revolution will be a rise of organization and intensity of worker agitation and national liberation movements, caused precisely by the failing power of the US, taking the reigns of power from the collapsing US state. As the US loses its grip on the international proletarian labor pool, which its currently doing a fantastic job at, the American bourgeoisie will have no choice but to bring back all those contradictions they successfully exported a century ago in a desperate attempt to retain their profit margin. Labor laws will be stripped, mass shootings will skyrocket, police repression will be rampant, and Republican/Democrat political theater will go bananas as they try desperately to get Americans to focus on literally anything but class consciousness. This all in an attempt to keep the bourgeois way of life intact.
This ironically is the best cocktail of ingredients to induce revolutionary fervor. With the USD inflating to Weimar Mark levels, a complete loss of international support and legitimacy with Europe falling to pieces over Ukraine, structural break down of the government due to political infighting, and a non-existent productive base leading to economic disintegration, the most expensive military in the world will be left with no supplies, no organization, and no soldiers (you really think US soldiers will kill their own countrymen if their not at least getting paid?) At that point the US will either have disintegrated into chaos or, if we're lucky, have an organized proletarian movement take the reigns of power locally and nationally simply by being the only real organized political force left.
I give it 15 years tops
You're definitely right in the short term. There's no possible way a revolution would succeed in America as it stands right now. Things will get really bad and massive repression and open fascism will likely follow. But that can't last long. The US has almost no internal economy. Post WWI Germany at least had a relatively intact industrial base for the Nazis to seize and send into overdrive to fund its military and terror campaigns. If the US's resource supplies from puppet states in Latin America and Africa and it's manufacturing bases in China, India, and Vietnam get cut off, US society will slam to a halt. And I think this likely will happen once countries are certain the US can't retaliate against them for resisting anymore, which is coming soon enough. People won't be able to buy food or basic supplies. The military won't be able to get fuel, bullets, or jet/tank equipment. The US won't be able to have the military/police successfully do anything, be it attack its own citizens or any foreign nation. It might flail out before all this occurs and try to fire nukes at China or something, but they'd likely all get intercepted and America invaded. Call me overly optimistic but I think it will be quite shocking how rapidly the US state falls apart, and stays broken, without it's imperial spoils