Did the Libertarian get "turned" at school and/or through friends?
My progeny and their family are all Conservative. They live in a RED state, so though their votes count, it's sort of the same situation in reverse.
My libertarian son got that way by being an Econ major at a college in the UK, I believe, although he always trended “left” from a very young age. Doesn’t seem to believe much in borders/the nation-state, abandoned Christianity, and likes crypto.
He’s a good guy though, and married, and smart and otherwise reasonable. Maybe after he has kids he’ll trend a bit more right.