“The time to stop him is in the primary.”
With the loony bin of dems and gops you described?
The “Opposition” needs to organize around one candidate.
Also, the “Opposition” needs to start taking over the party starting at the precinct level working up. Voting out the “Old Bulls” both in the party organization and in the county commissions, sheriff offices, and state legislature. It’s being done elsewhere it can be done in SC. It takes time, focus and persistence. It will not happen on its own or overnight.