I can respect that. I more or less agree with you. My doubts mainly form from a few things.

• The Leaks (not necessarily hacks at all)happened when Bernie and was still in the race to Wikileaks. So months before Trump won.
• Hillary and others were busy saying the elections could not be rigged, and that people were nuts for suggesting it UNTIL SHE LOST.
• They did not go for the HACKING angle first, that was like they third push to justify the loss.
• Wikileaks state 4 months ago (almost 5 now) that they did not get the leak from Russia or a State. That does not mean the leaker that provided them the information did not.
• After they kept aiming the scapegoat gun at anything they could, and they started finally saying the things they were previously saying were ludicrous (as long as their opponent was saying them). My bullshit radar was already on high alert. This is not as a Trump supporter, as I supported neither Trump or Hillary and fully expected her to win.
• Without actual sharing of the information that could PROVE the hacking to tech people like you/I that actually deal with this information, classified does not cut it. If it is classified and can't be shared then they shouldn't be feeding news stories about it to the news. It is firing people into activity and decisions on what could very possibly be totally false information. IF they need to keep it classified then they need to keep they mouth shut as they typically would do with classified information, and investigate it, capture people, etc.
• If you've studied propaganda, World War 2, and any time since then this seems like classic propaganda techniques. It is working on a lot of people. Others it is not working at all, and that may not be because they know tech like we do, but simply because they tend to not believe the government on anything. I can't say.

So is it possible the Russians hacked the DNC server... Sure. I ask you how can the FBI know this with proof though when they have not been given access to the DNC server?