This is the question many people would like to have answered.
No simple answer exists, Fivethirtyeight is pretty good at poll analysis and did look at it. They did not come to a clear-cut solution. The article is somewhat extensive with some data. Political geeks will argue over it for years.
How did Hillary Clinton blow a 7-percentage-point lead over Donald Trump in the final month of the campaign? Much of the post-election analysis has revolved around FBI Director James Comey’s letter to Congress on Oct. 28. Less attention was spent on the role that WikiLeaks played. Until, that is, news broke that the CIA thought Russia actively tried to help Trump win; figures connected to the Russian government allegedly hacked Clinton campaign chairman John Podesta’s emails, which then found their way to WikiLeaks. So what effect did WikiLeaks have on the election?
https://fivethirtyeight.com/features...llary-clinton/