The protests do have a negative impact because

1. It causes conservatives to double down ideologically and raise the temperature of urgency. They feel more obligated to mobilize in November.
2. Biden won off an exceptional primary surge of elderly suburbanites. Urban protests makes those people nervous and instills doubt in them, making them gravitate toward more decisive "law and order" proclamations that are more identified with conservatives.

But the electoral prospects of a conservative Democrat shouldn't matter to us whatsoever.