"Progressives should not make the same mistake that Ernst Thälmann made in 1932. The leader of the German Communist Party, Thälmann saw mainstream liberals as his enemies, and so the center and left never joined forces against the Nazis. Thälmann famously said that ‘some Nazi trees must not be allowed to overshadow a forest’ of social democrats, whom he sneeringly called ‘social fascists.’
After Adolf Hitler gained power in 1933, Thälmann was arrested. He was shot on Hitler’s orders in Buchenwald concentration camp in 1944."
The solution is a Multi-Party system with coalition and then compromise out of a position of power. We need to accept that in almost all societies the real left are a minority. Humans don’t like the socialist ideas even if it benefited then Right now because they dream of escaping poverty and to then be better than others. If we destroyed the class system they’d have no chance to some day be better than other people. I believe this drive to get ahead is part of human nature and only few are able to fight it and think in the benefit of the whole.
So there are 2 options:
Is a revolution, violent and ends in establishing an authoritarian government forcing your beliefs on the majority of people which kinda goes against my democratic beliefs and the right of freedom
Go into politics. In europe it would be voting very left and gain enough votes to join a coalition to make the centrists enable more and more socialist policies. This worked very well in some countries like early Germany, netherlands and a big portion of Scandinavian countries. In America basically the only option would be to join the democratic party and advocate socialist policies from within like Bernie sanders is trying for example. Vote more left in the primaries to try and gain influence.
After that when it comes down to voting either of the 2 parties though you probably need to accept the current majority in the democratic party in order to not enable far right.
The time to go more left is between big elections and from within. In big elections like the upcoming its time to set differences aside and unify for the lesser evil.
Never forget that a democracy is a rule of the majority of the population and not a rule of the best policies from your perspective. If you think: Fuck the majority, this is how the country should be run, you are not democratic.
This of course disregards the influence powerful people take in politics which is another topic and way more complicated.