I still see a lot of denialism on this point from the far-left (or the alt-left, depending on your favored terminology), which is a bit devastating to see as it essentially parrots the pro-Russian ideology of the far-right (both the alt-right and the neo-libertarian flavors). Green Party candidate Jill Stein is an especially pernicious promoter of this myth that Vladimir Putin is a poor, innocent, peaceful world leader who is being bullied by NATO (when in fact, Russia has been the aggressor since its annexation of Crimea in 2014).
DNC hack forensic evidence
Two separate Russian-affiliated adversaries were behind the attacks, according to a post-mortem by cyber-security firm CrowdStrike when the news of the intrusion first broke in early June, 2016. This has since been confirmed by other independent security firms including Fidelis, Mandiant, SecureWorks, and ThreatConnect as well as corroborated by analysis from Ars Technica and Edward Snowden.
At this point the US intelligence community is confident enough to formally accuse Russia of involvement in the hacks, and are currently investigating other breaches of voter registration databases in Arizona and Illinois as well as in Florida — the key battleground state from the 2000 election that handed GWB an unfortunate victory. Elsewhere, there is ample evidence of Putin’s extensive disinformation campaign being waged online (including several experiences I have myself witnessed), which is the continuation of a long through line of wielding propaganda as a tool from the former head of the KGB.