At this stage of my embittered middle-age, only three things bring me happiness: Duke losing in the NCAA tournament, the Yankees losing anywhere anytime, and progressives dogging each other with purity tests.

Is it possible for the most left-wing candidate in the presidential race, the great socialist hope, to fail a purity test?

Maybe so!

To clarify, by ‘the left’, I mean the lefty folks in my mentions telling me it’s fine to do Fox News because they have a ‘big audience’. So? Breitbart has a decent audience too. Write guest op-eds for them too? There has to be a hygiene line somewhere, doesn’t there?

— Mehdi Hasan (@mehdirhasan) April 16, 2019

Fox News will use these Democrat town halls to attract new advertisers which will help keep Hannity, Tucker et on the air undoing a lot of grassroots pressure on advertisers

— Dan Pfeiffer (@danpfeiffer) April 16, 2019

As you’ll see, Kos agrees. I understand his consternation, too: Sanders’s town hall on FNC last night was a smash success, and successful models tend to be imitated.

Sanders clocked nearly 2.6 million viewers from 6:30-7:30 PM Monday; that includes 489,000 in the 25-54 news demographic. Sanders logged the highest rated weekday delivery of the year in the news demo, and the second highest weekday delivery in total viewers among cable news networks…

Sanders’ town hall also outstripped FNC’s average in that hour by 24% in total viewers and 40% in the news demo.

Michael Brendan Dougherty congratulates Bernie on a minor messaging coup:

[H]is appearance on [F]ox showed that distinguishes him from other Democrats and particularly from Hillary Clinton. Many Republicans who watch Fox News and consume populist media can get the distinct impression that Democrats are just waiting for them to die. That was what was so damaging about Hilary Clinton’s “basket of deplorables” comment and her implication that Trump supporters will have no place in defining American life going forward. Sanders believes in his message so much, he wants to pitch it to you just before you settle in for Tucker Carlson Tonight. That’s to his credit.

Kos concedes that it was a coup for Sanders personally. His objection is that it hurts the Democratic Party by mainstreaming Fox among liberals, undermining the left’s goal of making the network an unsafe space for advertisers. That’s a potent criticism potentially against a candidate like Bernie who’s conspicuously refused to identify as a Democrat, a point that’ll be used against him in the primaries by his opponents to turn rank-and-file Dems against him. Trying to convince members of the party faithful who are Bernie-curious that they should look elsewhere for their nominee? Attacking him as a selfish politician who doesn’t care about advancing the broader left’s goals isn’t the worst way to do it.

But there’s a problem. As I said, success breeds imitation, and Bernie’s success on Fox last night is destined to make it safer for some candidates to accept a little free publicity from FNC as well. In fact, it’s already happening:

Democratic presidential candidate Pete Buttigieg is in talks with Fox News about appearing in a town hall event on the network, a campaign spokesperson told The Hill on Tuesday.

The spokesperson, speaking a day after Sen. Bernie Sanders (I-Vt.) appeared on a Fox town hall, told The Hill that “reaching out to the Fox audience is something we intend to do.”

With Bernie and Buttigieg paving the way and proving that one can survive a Fox appearance with their progressive cred intact, it’s a cinch that some of the dark-horse candidates like Eric Swalwell or Andrew Yang will follow their lead and accept an invite if that’s on the table. That’s exactly what Kos is afraid of: By swiping at Sanders here he’s trying to warn copycats who have less dependable fan bases than Bernie and Mayor Pete not to make enemies of “the team.” Which creates a dilemma for candidates who’d also like some free exposure but aren’t in the same nothing-to-lose boat as Swalwell or Yang in potentially alienating Kos-style Democrats. What does a Beto O’Rourke or Kamala Harris do if Fox offers them a town hall and an hour in front of, say, two million people? My guess is they say no, mainly to preserve their ability to use the “team player” attack line against Bernie. It’s not as if Fox’s white working-class audience is a core part of the voters they’re targeting the way it is for Sanders, after all. They can afford to decline in the name of purity.

I think Kos is right, by the way, when he said elsewhere in this interview that Fox’s audience really isn’t persuadable by Democrats, even one like Bernie who caters to blue-collar whites. They’re rock-solid Republicans who feast on attacks aimed at the left every night in Fox primetime. Sanders probably didn’t succeed in flipping any of them. Buttigieg won’t either, although I think he figures that anything that introduces him to more voters at this point improves his chances. He’s exceptionally good in interviews, conveying his intelligence and the sense that he doesn’t find populist righties “deplorable” the way Hillary Clinton did. If he emerges from a Fox town hall not having won any votes but having cemented the sense even on the right that he’s an impressive mild-mannered guy, I think that’s a win for him. He’ll risk some “team player” grumbling for more positive name recognition.

WATCH: Should more Democrats follow Bernie Sanders and reach out to the Fox News audience? #MTPDaily@Markos: "It's actually a smart move for him personally, but it just goes to show once again that he's not a team player." pic.twitter.com/R3jFY5wPqh

— Meet the Press (@MeetThePress) April 16, 2019