Polls are already showing that the goodwill gained is going away because the republicans immediately started blaming Biden himself for planning and encouraging the assassination attempt. Trumps numbers went up, but are going back down now. One republican pollster admitted that people are just tired of Trumps bullying and lying, so he gains nothing from this from moderates. The only result is that his fanatic supporters are becoming.. well, more fanatic.
One side hates his guts, the other side worships him. The middle is disgusted with both candidates and is trying to wrestle with do they want il duce part 2 or an even more senile Ronnie part 2, and this attempt does nothing to sway the middle after how he and the republicans are responding to it. He still might win, I don't know, but this event didn't do it.