My impression is that the left just kind of petered out around the 1980s, because there was a broadly felt sense that "everyone is middle class now" - leaving the US with a "leftist" party that really was more "moderately conservative", and a Republican party that was fumbling its way closer and closer to fascism, via "populist" conservatism.

To quote the usual phrase: Republicans are the reason things got worse, Democrats are the reason things did not get better. I think that's what people are getting at. If you want to get out of this situation, the US needs Democrats who actually want to make things significantly and noticeably better - and Democrats who stand in the way of that, are part of the problem.