If the primary were being held today, with the candidates polling like they are today, I would probably vote for Sanders. This would not be because I believe him to be a viable candidate, but because I believe him to be the most viable counterpoint to the most likely candidate (Biden).
On the subject of Biden, he has proved to be surprisingly resilient in spite of the damage Harris did to him in the June debates. I’m also sure he’s likely to be a Hillary-esque disaster, and if not that, a highly ineffectual president.
He’s just the sort of candidate Hillary was: a “safe” and “responsible” moderate choice who will turn off a chunk of the more progressive Democratic base while at the same time failing to enthuse enough crossover voters to win. If, despite that, he wins, the Republicans will make mincemeat of him once he’s in office, because he harbors laughably naïve delusions about bipartisanship being possible. Sorry, Joe, that era is dead. Republicans will absolutely despise you, and there is nothing you can do to change that.
Buttigieg gets it. As he said in the debate:
It is time to stop worrying about what the Republicans will say. If we embrace a far-left agenda, they’re going to say we’re a bunch of crazy socialists. If we embrace a conservative agenda, you know what they’re going to do? They’re going to say we’re a bunch of crazy socialists.
Buttigieg is still a moderate, not a progressive. But at least he’s far less deluded about the nature of the current situation than Biden (who seems to be living in the past) is. To some degree, he also realizes the old political center is dead (check out his plans for restructuring the Supreme Court). Alas, he’s not even polling at 10% right now, which means odds are he’s an also-ran. O’Rourke, Booker, Yang, Gabbard, Delaney, etc. basically are also-rans, and as such should be seriously considering leaving the stage.
On the subject of naïveté, we have both Sanders and Warren (and to a lesser degree Harris) going full steam ahead on single-payer health care despite the enormous pitfall of the unpopularity of making private insurance illegal, and the enormous stupidity of advocating the centralizing of something in the Federal executive branch while we’re simultaneously living a real-life example of the dangers of doing precisely that.
Anyhow, back to the subject of also-rans and viable candidates. Absent some unforeseen development, the Democratic Party nominee is going to be (in order of decreasing likelihood) Biden, Sanders, Warren, or Harris. Note that Biden currently has a huge lead, almost twice as much support as the next most popular candidate (Sanders). Therefore, odds are the nominee is probably going to be Biden.
Given that Mr. Establishment is the likely candidate, I would want Mr. Anti-Establishment, the outsider-ist candidate who isn’t an also-ran, to have as much influence as possible, to force Mr. Establishment to do a measure of triangulating to the left. That anti-Establishment candidate is clearly Sanders; he’s not even formally a member of the party under whose banner he’s running!
Of course, this is all a hypothetical. The primary is not being held today, and when it is being held, the candidates will doubtless be polling differently than they are today.