If Joe Biden ran as an explicit brake on the Democratic party’s left and won the Democratic nomination that way, it “would produce fury on a scale that far eclipsed the pro-Sanders anger in 2016 and guarantee a strong 2020 showing for Jill Stein’s grifter left (if not a more sincere alternative),” writes Ross Douthat.

He might be right. It may be worth noting, though, that the best recent showings for a left-wing third-party presidential candidate came during the eighth year of a Democratic presidency. In 2000, Ralph Nader got 2.7 percent of the vote, and Stein got 1.1 percent in 2016. It may be that a significant fraction of left-wing voters gets disillusioned with Democrats and complacent about the Republican alternative after too much time in power. Keep in mind, also, that some left-wing voters may have thought that Donald Trump was so sure to lose in 2016 that they could indulge an ideological gesture. That kind of thinking seems unlikely to be as prominent with an incumbent Trump on the ballot.