Party organization + good messaging has a snowballing effect through recruitment. It looks impossible because it feels like you'd have to personally convince hundreds of people, but that's not the case.

The difficult part is joining/creating parties willing to have coherence and discipline, but luckily that's a lot more tractable than convincing every lib to stop being lib.

Also, you'd be surprised at how amenable people are to large swaths of socialist thinking, they've just never been exposed to it. Literally never. Those are opportunities.