When has a sizable portion of the Democrat base ever sat out or voted third party? Sure, individuals may have tried once or twice, but the point is that it needs to be a sustained effort that's not being actively discouraged by the rest of the voters. By calling them Russian trolls or bots or idiots or whatever else. I think it's way more idiotic to keep doing the same thing over and over, keep watching the party shift further and further right, and keep saying "theres no other choice! Game theory! It's functionally a two party system! Not voting for Democrats is the same as voting Republican!". That's such a short-sighted point of view, and only works if you look at each election in isolation, not on a long enough timescale. If you're not willing to do it for yourself, maybe do it for the voters 3 decades from now.