If he wants to effect change in his life time, he will have to do it within the Dem party.
If he is willing to allow the GOP to have control for the next 1-3 elections, he could force a significant restructuring on the left, which might lead to his party replacing the existing Dems. But, that would also change the GOP. Would be a very interesting next 20 years during all that change. Previous transitions took that long, but maybe things would change faster in the information age.
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