"This is disproven by the fact that strong pluralities of Republicans supported almost identical policies under a different president."

Well, look, I think you are casting people as acting in bad faith but it is a lot more complicated than that, for example, different nuances in how the policies are crafted, promoted, or enforced; learning from what are viewed as mistakes; or different sentiments among the population at large. It's hard to say because you haven't given any examples.

I'm also not sure if you mean congressional Republicans or individual voters or activists or whathaveyou.

But I'm not really interested in defending Republicans any further than this here.