You present no data to prove this! Why? Because it's a total lie, that's why.

In fact, a lot more Hillary supporters voted for John McCain in 2008 than Bernie supporters voted for Trump in 2016.

The people who didn't vote in 2016 were not leftists - they were generally apolitical, poor, and people of color. https://theintercept.com/2020/04/09/nonvoters-are-not-privileged-they-are-largely-lower-income-non-white-and-dissatisfied-with-the-two-parties/

Of course, you made precisely zero attempt to actually find out any facts.

Mainstream Democrats relentlessly insult and belittle centrists or the few of the actual left that remain.

Then they run some horrible candidate who proves wildly unpopular, lose, dust their hands off and say, "It's those progressives! Hillary Clinton was only the second most unpopular Presidential candidate of all time, she should have won in a landslide."

Good luck insulting your potential voters! I'm sure that will work just as well for you in 2020 as it worked in 2016.

Me, I moved to the Netherlands in 2016. Right-wing Democrats like you convinced me that America was going to lose to the Fascists and so far you guys are doing even worse than I expected.

Good luck with your collapsing society! I'm sure you'll be blaming Bernie all the way.