Humans are thoroughly irrational creatures. All our supposed rationality is a rickety structure, built as it is on foundations of illogic. (See Sociological Insight by Collins.) Mostly we decide first, and then engage in motivated reasoning to find rationalizations for our decisions. (Not you, of course, or me...)
Humans do hero worship. (That there should even be such a thing as a celebrity-- someone who's famous for being famous-- is telling.) It's natural, even if it's irrational. It is a modern equivalent of "Who's popular at court?"
And we define ourselves by our heroes, we identify with them, they are our avatars. "Leave Brittainy alone" is "Leave me alone, stopping picking on me."
People at political rallies are a lot like people at sporting events, or people at a concert: identification with a hero, solidarity with the crowd based on shared identification with the hero.
A certain type of person is interested in politics and policy. Let's call them Politisports Fans. Politisports Fans like to talk and argue with each other about politisports. There are relatively few of them, but they don't realize how rare they are because they mostly only talk to each other.
The vast majority of people, unlike Politisports Fans, know little and understand less of government and politics, though many of them vote. Let's call this group Regular People. Regular People don't talk to each other about politics much. They talk about sports, the weather, food and celebrities. That kind of stuff.
What's funny is that Politisports Fans try to make sense of regular people through measurements appropriate to measuring Politisports Fans: What policy is important to them? What do they think of tax reform? Pollsters poll them and people answer, but it's so much fluff. They pick their heroes and then learn to repeat some slogans: Taxes are too high! There's too much regulation! Yes, we can!
The election, for Regular People, boils down to: Who is your favorite gladiator, Clinton or Trump?