CrowdStrike has figured prominently in the Democratic National Committee cyber attacks and the attribution of those attacks to Russian intelligence services. On March 20, 2017 during testimony before congress, James Comey stated "CrowdStrike, Mandiant, and ThreatConnect review[ed] the evidence of the hack and conclude[d] with high certainty that it was the work of APT 28 and APT 29 who are known to be Russian intelligence services."[20] However, the FBI did not independently verify these findings because the DNC refused to give the FBI access to the server.[21]
https://en.wikipedia.org/wiki/CrowdStrike
There is an additional leap involved. Assume that some Russian originated virus was infecting DNC server.
That does not mean the "infector" got access to the DC e-mail; nor does it establish that this is the source of Wikileaks, even if some Russian hacker DID have the DNC emails.
The chain of reasoning is "Russian virus on DNC server, therefore Wikileaks got the DNC e-mails from Russia." The gap in evidence is clear.