Most people who dislike Trump don't dislike him because he's Republican, most don't even believe he's a true Republican, or conservative, or evangelical. He was a New York Democrat in the past, supported gun control, abortion, etc, therefore his ideological core is questionable to say the least.

What people dislike, beyond the sheer incompetence and pathological lying and bragging, is a tendency to play to the worst aspects of the crowd, for narcissistic reasons. That is, people are upset because they believe Trump is a person who will stoke up division for no reason other than it gets applause and attention, and often, the "heel" in WWE Wrestling parlance that Trump uses turns out to be the least powerful.