It’s not the evidence,rather the seriousness of the charge.
Or more like the stridency of the charge. Sometimes the charge itself over which we are supposed to get all worked up is a nothing. It’s like making a whole campaign against someone because he wore the wrong color tie to a press conference. The Left can use up all the air with such a charge and in truth it works to some extent. People get a vague felling that there is something wrong because of all the yelling even they know the charge is obvious nonsense. They get a feeling that maybe it is sense but they just don’t quite grasp it.