My understanding is that it's far from clear how a case again Assange/wikileaks would play out in court. Like the article mentions, the New York Times and others have published classified information repeatedly -- how can Assange be indicted but not the NYT? Assange also isn't an American citizen and he hasn't leaked information himself, just published it. I think there's a good chance Assange would be acquitted.
I also think it's a bizarre exagerration to argue that an attempted prosecution of Assage would result in "broad new powers to put Trump’s media 'enemies' in jail".
Don't get me wrong -- I don't much care for Assange. It seems to me that there's a lot of hot air coming from him and he appears to have quite an ego. Also, though I understand there is disagreement about this, I think countries keep secrets for a reason and I consider it naive utopianism to expect everything to be brought into the open. In an ideal world, sure, but the world is not ideal.
While I don't think Assange/wikileaks are necessarily "siding with Russia," I do think that Russia has made use of wikileaks. Wikileaks is heavily promoted in Russian propaganda, and it seems at least plausible that Russia could obtain information and leak it through wikileaks. This is a problem for wikileaks: if you're all about freedom of information and you make public everything passed onto you, it's totally possible for state actors -- the same state actors whose behavior you find reprehensible -- to use you as a tool to further their own interests.