There's plenty of non-classified evidence that goes much further than the joint Intel report goes, and was available before it.

It's kind of disappointing this isn't widely understood, but I guess politics gets in the way. Anyway, feel free to share this:

2014 report into ATP-28: https://www.fireeye.com/blog/threat-research/2014/10/apt28-a..., presenting pretty compelling (if circumstantial) evidence that group is Russian state backed.

(July) 2016 report into the DNC hacking, showing it was first breached by ATP-29 (The other Russian state backed hacking group), but the leaks almost certainly came from a second breach by ATP-28 later: https://www.crowdstrike.com/blog/bears-midst-intrusion-democ...

One can of course argue that this is all a conspiracy. However, the fact that this first report was publicly available in 2014 gives some protection against the idea that it is motivated by US internal politics, and the second was also before the election actually occurred.