Republicans are told they have to support them because "they can win".
"told they can win."
That's part of the problem, but sometimes there's a district where only a relatively nonpartisan or relatively moderate Republican can win, so we have to take that. However, the powers that be in the party should be on the lookout for WEAKLINGS and IDIOTS and SELLOUTS, which are not necessarily the same thing as moderates or people who are willing to work with Rats. With careful skills, such individuals can often be identified early in their careers
by sophisticated higher-ups in the GOP. Their careers can then be aborted before they ever get into any significant office, reducing the chance that they can come out of the blue and win election to the legislature or Congress. By its nature, this is unfortunately something that needs to be done behind closed doors by undemocratic, top-down processes, by leaders, not voters.