Since Trump is a narcissist, he assumes the more that people see him, the more they will like him, so he’s unafraid of ad-libbing. In fact he’s terrible, but still his “indiscipline” communicates a kind of openness, he his what he is he has nothing to hide.

Kamala’s campaign is professional, “disciplined”. Which does prevent potentially costly gaffes! But the public does perceive the stage management, knows she is not “letting it all hang out”, wonders then if she might have something to hide.