“Let’s do a pledge. Who likes me in this room?” Trump asked the crowd at a rally in Orlando, Florida, which was frequently interrupted by protesters. “I’ve never done this before. Can I have a pledge? A swearing? Raise your right hand.” The Republican presidential front-runner then proceeded to get the audience to repeat after him. “I do solemnly swear that I, no matter how I feel, no matter what the conditions, if there are hurricanes or whatever, will vote on or before the 12th for Donald J. Trump for president.”
This is "the cult of personality" in politics, and it does not turn out well. Taken further, it's not just asking for a promise to vote for a person one "likes" but an oath of loyalty to the individual. One famous one went "I swear eternal allegiance to Adolf Hitler and to those designated by him unbroken obedience." More significant were the oaths sworn by the Wehrmacht, German civil servants, and the SS, "swearing loyalty to the person of Adolf Hitler rather than the nation or the constitution."
In the United States we pledge allegiance to the flag in a relatively recent and not particularly binding ritual of civic loyalty. When we "solemnly swear" or affirm in the United States it is to support and defend our Constitution. Donald Trump is casually, almost flippantly messing around with that tradition. Combined with Trump supporters' supporting the man and not his policies, that is a very bad sign.