When Donald Trump’s political credentials as a Republican and/or conservative are challenged, he likes to remind people that Ronald Reagan was a Democrat once and managed to evolve over time. Except that Reagan’s conversion was real and he had two terms as governor of California to prove his bona fides before he ran for president as a conservative Republican. As Reagan campaign manager Stu Spencer and speechwriter Ken Khachiagin note in a Real Clear Politics piece: Yes, Ronald Reagan migrated from being a liberal Democrat to the gold standard for conservative Republicans. But Reagan’s views evolved over four decades’ worth...