In modern politics, simple messages tend to work a lot better than nuanced ones (which is a thing that Donald Trump masterfully exploited). “X is good/bad” is a much simpler message than “X is good, but only if it’s X1, and not X2″ and having primary opponents claim “By supporting X, [politician] argees with the evil other-siders in their support for X2! [Politician] is an our-sider-in-name-only!”
In modern politics, simple messages tend to work a lot better than nuanced ones (which is a thing that Donald Trump masterfully exploited). “X is good/bad” is a much simpler message than “X is good, but only if it’s X1, and not X2″ and having primary opponents claim “By supporting X, [politician] argees with the evil other-siders in their support for X2! [Politician] is an our-sider-in-name-only!”