The Weimar Republic had to fight dirty to keep it from happening. They had to empower the Freikorps to violently break up leftist strikes and rebellions. Empowering the same extremist that would attempt to first overthrow them during the Kapp Putsch and then eventually successfully overthrowing them when they all joined the Nazi.

Political assassination of leftist politicians were overlooked and ignored, while attempts against right winged politicians were demonized and harshly punished. It's very reminiscent of how the current US government treats right winged violence compared to the left.