As I recall, Reagan was a Roosevelt democrat. Campaigned for him and probably gave him money as well. The rest of your sentence is pure snark.
Sure, forty years before he was elected president. Reagan had plenty of time to demonstrate in deed and in words his conservative ideals. Harriet Meirs hadn't. Reagan was governor of California. Harriet had no time on the bench and accomplished nothing.
Bush's actions in nominating her and in pushing amnesty are both inexplicable and despicable.
What makes you think that Miers had a Reagan-like change of political philosophy?
Miers was Bush's legal adviser. Why do you think it's a "snark" to expect that her legal advice to the president was not "enforce the immigration laws, Mr. President!"?