This is the result of constant conspiracy pounding by virtually every mainstream media outlet and tons of social media propagandists like Louise Mensch.
Via Daily Caller:
A majority of Democratic voters think Russia literally rigged the vote in the 2016 presidential election — an outlandish conspiracy theory with no evidence to support it.
The latest Economist/YouGov poll found 58 percent of Democrats saying that it is “probably true” or “definitely true” that “Russia tampered with vote tallies in order to get Donald Trump elected President.”
That number is up six points from December when 52 percent of Democrats said they thought Russia tampered with vote tallies.