I think it is pretty easy to see why Russia would want to see Trump get elected because that would spell trouble for the American democratic system when a mad man get elected to power he has no idea what to do accept followed flawed narcissistic patterns of lying, and make up stuff to prove your a winner and not a loser.
Get a guy like Trump president who is easy to manipulate because of his narcissistic world view and force him into one humiliation after another using his narcissistic rage to lead him like a ring on the nose of a bull.
Think that is exactly why, but I could be wrong, Trump definitely brings to light some flaws in the system we have for who can be a candidate for president. And the need of a proper education and psychological mental health for the sake of the country's well being. Especially to such a high office as President some kind of qualification must be met with complete transparency to keep nut cases like this from even thinking of running.