US didn't collapse after Vietnam, why would they collapse now. People who are politically powerless hope for catastrophe but the left in most countries no longer have the mass base and political power to do anything when the opportunity presents itself. There is a lot of work to be done.
a large part of the ussr's dissolution was that citizens of the eastern bloc wanted the luxuries and consumer goods of global north capitalism. the us doesn't have this issue - no average american is thinking about how much better life would be if they just adopted socialism with chinese characteristics. its just capitalist realism - in the ussr, there was an alternative that was (unjustly) idolised. the usa doesn't have that (ur succdems dont count)