This link goes into detail about the perspectives of some whites on the BLM movement and how Trump played on those fears and represented a solution to growing minority influence (presumably at the expense of whites) in the wider culture. This also needs to be understood in the context of disruptive BLM protests as well as the white nationalist protests in Charolettesville.
>yet any adversary of the United States could conceivably benefit from "sowing division"
This is just so obtuse on so many levels.
None of these claims have any actual evidence backing them, and when claims can be sourced the sources collapse under examination; see my article above.
But we shouldn't need to deeply analyse academic papers to see that this narrative is nonsense. It is just not internally consistent. Putin had clear reasons to want Trump to win, that I accept. So why would his staff post things supporting Clinton? There is no logic to this idea whatsoever, and it's not where the narrative started.
There's a deeper issue here too. It paints the posting of political talking points from both sides of a US election as generic "sowing division". That is a world view that is quite totalitarian. I could describe it equally as "invigorating the democratic process by increasing interest in the election" and be no less accurate.
a large part of his support was due to the fear created by the appearance of growing civil unrest
You haven't shown that, you haven't even laid the groundwork for that. It's actually the first time I've ever seen such a claim. Most analyses of why he won point to the weakness of Clinton, his policies in immigration and trade deals, his opposition to political correctness and so on. Not "the appearance of growing civil unrest".