“You left out an important caveat. Is the Republican a moderate or further to the right? This is a critical difference because the party base has worked to shun moderate Republicans, making the party home to ideologically pure and thus intellectually dishonest conservatives.”
This is really a side-issue but it isn’t the party base that’s doing that. That’s a consequence of the influence of the right-wing Rage Machine that is the communications apparatus of the American right and plays to a fringe that is actually a minority within the larger Repub voter base. Congress is particularly sensitive to these machinations because Repubs have been very corrupt and have spent years gerrymandering themselves into safe districts. They aren’t afraid of a Democratic challenger; they’re afraid Fox News is going to call them a RINO then begin campaigning for a more extreme primary challenger.