It makes him a martyr. Biden was already an extremely weak leader with a massive public perception problem. Trump surviving an assassination attempt while defiantly pumping his fist in the air is the clarion call for Amerikan Fascism.
Biden was already losing in every single swing state. I believe his existing chances before this event for winning reelection were somewhere around 10% at best. This obliterated those chances entirely. The average person is dumb as fuck, and they will vote for strong man leadership. It is a generational mind virus that rises up over and over again in the human psyche. This generation will be no different.