Question: Why doesn't the Democratic Party employ this same tactic with a candidate on the far left?
Don't EVEN try to tell me that Bernard Sanders is an extreme lefty: In Europe, he'd be slightly left of center, fitting in with Labour Party pre–Tony Blair.
For that matter, there was nothing extreme about Dennis Kucinich or Jesse Jackson. The Democratic Party used them for a different purpose, showing the nation that there is room in the Big Blue Tent for progressive views, and then gently telling the nation that progressive candidates are unelectable.
But "extreme" is all a matter of perspective, innit? Plenty of Republicans view Hillary Clinton as the second coming of Trotsky, and President Obama further left than that.
Jello Biafra is supporting Bernie this year. When Jello ran for the Green nomination in 2000, he ran a fairly quiet campaign, and he all but withdrew when Ralph Nader announced his candidacy. I'd love to see Jello run as the Democrats' answer to Trump, spewing things just as outrageous but without all the racism/sexism/ableism/sectarianism etc.