Bernie Sanders has never run for office as a Democrat. Even when running for the Democratic presidential nomination in 2016, he refused to make the simple statement that he was a Democrat. The closest he would come is to say he was running for the Democratic nomination.
There is a good reason for that -- that he is NOT a Democrat and doesn't want to become one. He reiterated that last Sunday, when he told Fox News that he would be running for re-election to the Senate in 2018 as an Independent -- not as a Democrat (even thought the Vermont Democratic Party begged him to run on their ticket).
Sanders said:
“I am an independent and I have always run in Vermont as an independent, while I caucus with the Democrats in the United States Senate. That’s what I’ve been doing for a long time and that’s what I’ll continue to do.”
I hope this ends the talk of his running in the 2020 Democratic primary for president. If he is ashamed to be a member of the Democratic Party, then he should stay out of party affairs, and that includes the party primary. The party has plenty of good candidates (including good progressives) that are proud to wear the party label -- and one of them should be our standard-bearer in 2020.