It means they haven't been paying attention to the "big picture" of what's been happening in America for the last couple decades.
What does it mean when people say trump has ruined the country? I don't like him any more than most ppl. I just don't understand.
People who say that are aware of the necessity of certain character traits that must be present in the leader of the country and which Trump fails to possess.
If you don't understand what I just said in that paragraph, then you have some insight into why a Trump supporter is a Trump supporter---they just don't get it,