> I don't understand why a new party has not formed to leave the batshit crazies behind.

Because when hyperspaces of political positions are projected onto a one dimensional binary, to choose to form a new party guarantees that one half of the hyperspace loses for a generation until there is a full party realignment. It is game theoretically sub-optimal in the short and medium terms, and depending on the effectiveness of your opponents, the long term as well.