I found this on Reddit, and I thought it was a pretty good summation:

I am trying to imagine a “presidential” library built in this thing’s honor… I cannot. What I think we should build instead is a library and museum dedicated to all the ways political power can be abused. The history of the past four years serves as a card catalog to that.

If his “legacy” will be anything other than the destruction of the Republic, it will be a hardening of that same Republic in reaction to the abuse it has endured and survived.