In Seattle, local elections are a contest between Socialists and Democrats. The former may not have much presence on the state or federal levels, but to say they don't exist in city politics is incorrect.
Also, the reason they can't succeed much beyond a few lefty cities is because they can't stop saying insanely stupid shit, like the suggestion that Boeing workers should seize Boeing factories and use them to make city buses instead of airplanes. Most of America doesn't go in for this kind of nonsense. This is a real example btw: https://www.kiro7.com/news/seattle-city-councilmember-elect-...
Also, the reason they can't succeed much beyond a few lefty cities is because they can't stop saying insanely stupid shit, like the suggestion that Boeing workers should seize Boeing factories and use them to make city buses instead of airplanes. Most of America doesn't go in for this kind of nonsense. This is a real example btw: https://www.kiro7.com/news/seattle-city-councilmember-elect-...