Once upon a time, Republican leadership were smart but evil people who fed lies to their base but understood that they were lying. Since they weren't actually delusional, they could choose the most politically useful lies and abandon the ones that didn't poll well.
Enough people believed their lies that the new generation of Republicans are True Believers. They've lost the ability to tailor their message to the political climate because it's no longer seen as just a bunch of crap to please the base, but TRUTH. Except that it's not actually true, so their policies fail.
This is the inevitable result of governing through falsehood. Objective reality can not be gaslit, and abandoning it never works out well long-term.