The answer may be July 24, 2016. That was when Clinton campaign manager Robby Mook, appearing on CNN, publicly debuted the "Russians helping Donald Trump" Big Lie to explain away and neutralize the publication at Wikileaks of thousands of embarassing DNC emails, especially about the party's official diss of Bernie Sanders' primary campaign. (Earlier iterations of "Putin Hates Hillary" welcome at firstname.lastname@example.org.) This Big Lie depended on more mythology -- namely, that the DNC emails came to public attention through a Russian "hack," not an internal "leak" -- the assessment not of the FBI, but rather another Democratic partisan, the DNC contractor, Crowdstrike.
This quickly morphed into "Putin hates Hillary."
Politico, July 26, 2016 - Julia Ioffe, Michael Crowley
NBC, July 27, 2016
Anonymously, NBC drops a load of pure propaganda.
Russian president Vladimir Putin's admiration for Donald Trump is rivaled by his passionate hate for Hillary Clinton, adding credence to the accusations that Russia is behind the damaging Democratic Party email leaks, former U.S. officials and experts told NBC News.
Putin carries a grudge against Clinton because she has publicly compared him to Hitler and expressed doubts that he has a soul.
Michael McFaul, the U.S. ambassador to Russia from early 2012 to 2014 said Putin "sees some of Clinton's remarks as a personal attack against him and the way he governs his country and how he conducts his foreign policy."
Like other former Obama administration Russia policy experts, McFaul said Putin-sponsored hackers were the most likely culprit in the hacking of 20,000 DNC emails that were posted last Friday by WikiLeaks. Cybersecurity experts also say mounting evidence all points in one direction....
And it doesn't stop. For example --
Los Angeles Times, August 3, 2016 - Masha Gessen on "why Putin hates Hillary."
And on and on.
The UK Guardian added a little spice to the Sanders angle on July 24, 2016:
A lot of pointing fingers in those headlines, and all the wrong way. With Sanders directing fire at the Wasserman-Schulz and Trump -- not Hillary Clinton! -- it would seem that perhaps he already had House No. 3 picked out. Might the headline writer have sensed the various fixes that were in? It may only be my imagination but "experts telling us" Russia was behind the hack almost conveys a desperate whiff of narrative creation. In any case, the Hillary campaign, its media forces, the DOJ, the FBI, the Obama White House, Fusion GPS, the Ohrs, etc., were all at the ready ...