"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."
Do not forget that in '32 the SPD backed Hindenburg… who then nominated Hitler as chancellor.
Thälmann was foolish, but even if he didn’t run, Hitler would still get into power. If the far right is strong enough, mere electoralism will not stop them. Fighting them must happen on the street level.
Genuine question - at what point?
You do it early (now), and you push swing voters away and hurt your cause.
You do it after they have power, and you’ve manufactured the pretext for your extermination.
Do it very early before they’ve metastasized. Do it after they have power too. The pretext already exists, they campaigned on it. Being a partisan is now literally a fight for your life.