I always thought Barack Obama was bad enough just as he stood, with no need to invent worse things about him. Nonetheless many of his opponents seemed unable to refrain from circulating things that were unlikely right out of the gate or refusing to accept reasonable explanations.
I said the same about Trump over a year ago: why make stuff up? why the need to make things worse than they are? It happens so often that it must be a human nature thing.
I grant that some of this must be tactical, if poorly so. People aren't upset enough about this guy! What if he's a actually gay? THEN they'll finally see and turn against him. What if he's a traitor? Finally, finally, people will see. Yet it is not only ineffective, it likely has an opposite effect. Criticise someone unfairly and even some of his or her enemies will start taking pity.
Which is why I conclude that some other need is being met when opponents exaggerate and demonise. It must be that the goal is not to talk about the other party, or politician, or public representative, or voters. It must be a way of talking about oneself. I've made it clear over the years what I think that is, but I actually don't insist on my special interpretation. It's pretty clear that something social rather than logical is up, however.