This 'fact' is repeated so often that, like so many things on the internet, it has become almost gospel, when what evidence we have indicates that it is not true.
We 'know', with the polling we have, a few things about the 2016 election and the Sanders/ Clinton/ Trump dynamic. We know that somewhere between 6-12% of people who voted for Sanders in the primaries ended up voting for Trump. We know, again with the estimates we have, that approximately 75% of Sanders voters ended up plumping for Clinton in the end, with the other 13-19% going to other candidates.
In isolation, this seems pretty shocking and like it would back up your point. If it wasn't for a couple of things. Firstly, despite the caricature that it was a bunch of disillusioned hippy democrats who voted for Sanders and then refused to vote for Clinton, what we see is that a lot of the people who voted for Sanders and then refused to vote for Hilary actually self identified as conservative or at least independent and actually were not members of the democratic party initially.
What we also know is that in 2008, about 24% of the people who voted for Clinton in the primaries vs Obama voted for McCain in the general election (ie more than double the Sanders voters who ended up voting for Trump).
As I said above, its an easy caricature to score cheap political points, used to explain a very complex topic but which doesn't have basis in facts.
Clinton lost in 2016 for many reasons. Is it partly because she's a woman? I'm sure that was an aspect to some. Was it also because she's a Clinton? Because she represented a continuation of the status quo that is no longer working for so many Americans? Because she has been held up as a bogey (wo)man by Republicans for years now? Because she is an almost uniquely bad candidate? Because she compaigned on continuing the current system and more important, campaigned essentially on not being Trump, whereas he, for all his faults and regardless of what you think of his actual policies, actually campaigned for tangible things? Clinton lost middle America and the rust belt and the Democrats did not bother actually appealing to voters properly.
I hope they have learnt their lesson because if they're still crying about Russia/Sanders in 2020, they're going to see another 4 years of Trump and most likely, an entire generation of a conservative Supreme Court.
Some references below if you want to get a bit further into it:
https://fivethirtyeight.com/feature...vote-what-does-that-mean-for-his-chances-now/
https://www.washingtonpost.com/news...lection/?noredirect=on&utm_term=.70748779b281