She was between 38 and 41 at the time (1987-1990). Her behavior was not the youthful sin of a teenager. It absolutely speaks to her character. It's nice that she eventually came around for whatever reason (maybe she thought it would advance her career). But that doesn't mean she's a trustworthy person.
Ronald Reagan was a Union president and Democrat into his 40's.
When you look at how the Republican party shifted from the 70's and 80's to the 90's and 00's it makes sense that it would leave many people behind. In fact, many former Reagan administration officials have either flipped or blasted the current Republican party.
This idea that you form a political mind in your 20's and then have to adhere to it the rest of your life isn't reality. It might be for some, but not for all. Party politics, demographic shifts and life experiences play a huge role on how you align yourself.
