When parties reverse their stance, supporters immediately switch their opinions
This is because the party will ostracize you if you don't conform. You can't survive in a liberal environment if you don't support abortion and you can't survive in a conservative environment if you support gun control.Your friends will argue with you, you'll be surrounded by memes making fun of people who believe what you do. There's incredible social forces to conform to the exact set of beliefs espoused by political parties, which are mostly set by corporate interests.It's a huge part of what the Republican party has struggled with: There's both the clear vision of conservative values and ideals... and Donald Trump. You can practically see on people's faces trying to reconcile their beliefs with party platform. And there's a massive amount of pressure to stay in line with everyone else.