The social democrats seek to compromise with the capitalists, which entails both a continuation of capitalism's injustices and a series of navigations through the political system that result in reform efforts being ineffectual. The Marxist strains do not present this pitfall. They represent a mission to build a breakaway society from the capitalist world. This has been accomplished with great success in numerous countries, and it can happen in America too.
Vote for Sanders in 2020 if you like, but it's time for the American left to move towards where it can truly succeed. It's time to leave Democratic Party appendages like the Democratic Socialists of America, and join communist revolutionary organizations like the Workers World Party. It's time to get involved in the social media efforts to radicalize progressive-leaning people towards communism. It's time to organize campaigns of civil disobedience which are centered around destroying capitalism. It's time to enter into a struggle that, if successful, will end with the ruling class seeing their entire power structure get torn down.