As I have written here before, elements of the Russian government want Americans to be divided against each other. I am not at all sure that they have had any success with this, since Americans already hate each other plenty, and even if it worked I am not sure how it would help them. But it does seem to be their aim.
In the light of this it makes perfect sense that Russian trolls and bots are throwing most of their weight behind Trump and Bernie Sanders. Surely a Trump-Sanders election would be one of the ugliest ever, and highly divisive. The two Americans have reacted differently to the news, Trump trying to deny it and Sanders accepting it; maybe that's partly because in a weird way it enhances Bernie's status by making him the most radical one.