As I understand it, people have a higher priority of maintaining affiliation with social groups (of which, political parties are an example) than they have a commitment to any given personal view. It varies based on context, the person, etc. and is obviously a complex phenomenon. But the default operating mode of the human being is to toe the line and to (genuinely) change their views based on where their self-identified in-groups are heading. Mob mentality, group think, etc. All sides of the same coin.
Rhetoric is empty. Always.