He won't care unless it is sustained.
I think it is reasonable for him to say he won under the rules. He has 60+ million voters, which is larger than the number who marched. (We both know she won more votes but that is irrelevant in the US system).
This energy was missing before the election. So now the Bernie folks who sat the election out see what happens when you avoid the choice between bad and worse. You run the risk of losing your democracy when you allow someone like Trump to take over.