Their base belief, I think, is that they, as a party, are entitled to govern. In a way, it's not even really about Trump himself anymore, it's just about using his "stolen election!" rhetoric as a groundwork for saying, "well, there are questions about the process, therefore these new restrictions are necessary." They can say with a straight face that "nobody" is denying the legitimacy of Biden's election while they line up to genuflect to the guy who denies it every day because there really isn't, in their minds, any contradiction- Trump's wild claims can be disavowed when they're recast as reasonable doubt, and still made to work for a party that doesn't think they need to win elections based on policy, they only need to not lose them through tactics.