The tact there being that party affiliation was more important than expressing their own choices, which isn't something that I understand in the slightest, especially as how centrist most candidates are.
In front of that, there's probably, "My parents were Republican. My family is Republican. My friends are Republican." And so on.
This isn't actually wrong, per se. It's a basic affirmation of trust in one's close network. Some people go to church without bothering to believe in God; they go because they've always gone and their parents go and their friends are there and they discuss the football game or whatever. They're passionate about things because all of their friends are passionate about it.