Their fathers and grandfathers (in the case of the Bush family) were prominent Republicans when the party was actually a legitimate political party. That Republican tradition predated the Moral Majority, the T Party, and Trumpism, and that pedigree prevents them from becoming Trump lap dogs.

The Congressmen/women and Senators who have gained elective office in the last 10-15 years really have no allegiance to the traditional Republican ideals. Their only allegiance is to get/stay elected, maintain political power, and if that means ignoring their oaths of office on a regular basis, then so be it.

So, yes it is remarkable that Romney is occasionally a stand up guy, but the truly remarkable thing is that he is such a stranger in a strange land.