If anyone is convinced Russia hacked the DNC, Jake Williams put together a talk[0] about the subject. If you follow him on Twitter, you'll realize quickly he wouldn't dump ice cold water on Trump were he on fire. The reality is there is just no way anyone could honestly claim with the certainty that the DNC has claimed that it was Russia.
[0]https://files.sans.org/summit/Digital_Forensics_and_Incident...