I don't think this will change much. Biden's response might. But politically, identity politics outweigh martyrdom in US. The right will get rightier and the left leftier. Most likely outcome IMO is emboldened like-actors on either side. Undecided voters could react maybe, but are they really that keyed in to be undecided in the first place?
I think you're right that this won't change much in terms of how people vote, but I believe it will greatly increase the tension between MAGA Republicans and everyone else. It seems probable that there will be some form of violent outburst from them.
Yeah, if nothing else trump will use it as post election legitimization for using lethal force in protest suppression and later, even more grievous acts. Not that he would have cared or needed it.