As to the Russian hackers thing, the 'Dukes' / APT29 group that have been mentioned have been around for a while and is most likely Russian based. Credible old-school security outfits have studied them for years.
See e.g.
The Dukes: 7 Years Of Russian Cyber-Espionage and
Group: APT29, The Dukes, Cozy Bear - ATT&CK
I'd say there's a reasonable case to be made that they're state aligned if not actually state sponsored. They may well be a free-enterprise initiative with tacit state sponsorship rather than spooks though.
There's also credible evidence that they've been fucking around with think tanks and political parties in the US and elsewhere, but it's as part of a pattern of activity going back many years. Not something they've just started doing since Trump. While they do seem to have become especially active in the US in the last 18 months or so, it's hard to tell if that's a higher level of activity or just more people paying attention to it.
See e.g.
PowerDuke: Widespread Post-Election Spear Phishing Campaigns Targeting Think Tanks and NGOs | Volexity Blog
As far as I can make out, the CIA claim is that this group (among others) have been fucking with the DNC, and were responsible for leaking embarrassing emails to Wikileaks, according to circumstantial evidence (e.g. the use of their characteristic techniques and tools)
This is supported by the analysis of the "cybersecurity and threat intelligence" firm apparently called in by the DNC
https://www. crowdstrike. com/blog/bears-midst-intrusion-democratic-national-committee/ (link broken due to xss warnings)
They also mention another probably Russian, probably state-sponsored group.
Group: APT28, Sednit, ... - ATT&CK
Operation Pawn Storm: Fast Facts and the Latest Developments - Security News - Trend Micro UK
https://www.fireeye.com/content/dam/fireeye-www/global/en/current-threats/pdfs/rpt-apt28.pdf
... who they say appear to have been acting independently of APT29/Duke.
Crowdstrike's claimed evidence is pretty much along the lines of that in the Volexity article I just linked. Persuasive enough within the limits of similar technical assets and operational method, but not conclusive and not really hugely useful for judging intent. It also doesn't show responsibility for the data breach in question but describes two independent groups, stealing authentication credentials and installing backdoors. If Crowdstrike do have forensics showing that one of these groups took the email in question and gave it to Wikileaks, they haven't published them and as far as I can tell, haven't specifically claimed to have any.
In addition, we've had claims of responsibility casting doubt on the attribution of the DNC data breach to Russian groups. Although doubts were immediately cast in turn on those claims by tech journalists. (Claimed 'Romanian and not Russian' hacker who can't speak Romanian properly etc) See e.g.
http://motherboard.vice.com/read/all-signs-point-to-russia-being-behind-the-dnc-hack..
My take on all of this is that credible security outfits have been reporting on APT28 and APT29 activities for long enough that I'm pretty sure they do exist, are most likely Russian and state aligned (especially APT28) and do go after political targets.
Whether they specifically gave anything to Wikileaks seems to me unproven, at least in the public domain. It's probable that these aren't one-offs, but persistent long-term collection activities of the sort that both of these groups specialise in. What I'm still getting my head around, is what else (besides publishing DNC email) is being implied by claims that Russian cyber-spooks were trying to 'influence US election'
I *think* what's really being argued is that the exploitation of the DNC data breach (and others) by parcelling out curated data sets to influence propaganda narratives around the US election was a Russian policy. This article summarises what I take to be the gist of that narrative
How Russia Pulled Off the Biggest Election Hack in U.S. History