The current Dems will stop any attempt at progressives winning anything. The first step has to be taking over the Democratic party. Find your local Dem party (every state and many cities/towns/counties have there own Dem party, and if they don’t, you can form one pretty easy) and start by replacing any conservative Dems there. “Luckily” these elections have extremely small turnout, and are relatively easy to win. These smaller Dem parties then elect leadership of higher level Dems like the DNC. Once progressives have control of the party we can choose what the party fights for and who gets support in primaries.

Alternatively, a highly popular candidate like Bernie or AOC could break from the Dems and start their own progressive party, but that would likely just lead to the Republicans always winning.