Bernie Sanders continues to dominate Donald Trump in head-to-head polling: he has now defeated Trump in twenty consecutive polls tracked by RealClearPolitics. And, in fact, except for a single outlier — a Rasmussen poll the firm describes as “a virtual tie” — Sanders has defeated Trump in every head-to-head tracked by the aggregator this cycle.

This isn’t a new trend; Sanders has been annihilating Trump in head-to-heads since 2015. But during the last election, pundits developed a standard explanation for why this wasn’t a big deal: Sanders, we were told, “hadn’t been vetted.”

Michael Tomasky, March 2016:

There’s one simple reason Sanders polls better against Trump than Clinton does, which is that no one (yet) knows anything negative about him. He’s gotten the freest ride a top-tier presidential candidate has ever gotten. The freest, bar none.

The New York Times, May 2016:

Toni Munkovic: Bernie Sanders does better than Hillary Clinton in polling against Donald Trump . . .

Nate Cohn: . . . Sanders just hasn’t faced any major attacks on his record. The Republicans have cheered him on against Clinton, whom they realize they’re inevitably going to face. Clinton never really attacked him, either . . .

Meet the Press, May 2016:

Chuck Todd: He is making a case . . . just showing how much stronger he is against Donald Trump than you are. Our own poll: he’s got a fifteen-point lead over Trump, you have a three-point lead over Trump . . .

Hillary Clinton: . . . I have been vetted and tested, and that puts me in a very strong position —

Chuck Todd: You don’t think Bernie Sanders has been vetted? You don’t think this one long year of campaigning, your campaign against him, has vetted him?

Hillary Clinton: Let me say that I don’t think he’s ever had a single negative ad ever run against him.

Even at the time, the notion that Sanders wasn’t facing a sophisticated and well-financed opposition campaign was fairly implausible outside of Clinton’s orbit.

But today, that argument has completely vanished. Sanders has now been in the national spotlight for more than four years — he has become so well known, in fact, that this has become the new reason to dismiss his performance in the polls. He has become a favorite target of Republicans on the Hill, in the media, and in The White House. And already in the Democratic primaries, Sanders has come under attack from centrist think tanks, corporate media, and other party rivals.

It’s not surprising that the “hasn’t been vetted” line disappeared after Sanders spent years in the national spotlight. But with the primary reason to dismiss his polling against Trump gone, one would expect the media to cover it quite differently.

That a self-declared democratic socialist could demolish the incumbent president in the polls stands directly at odds with the enduring conventional wisdom that the United States is a “center-right” nation and that the public is decisively committed to capitalism. This narrative has always dominated Democratic politics and mainstream media analysis, and even today it is still virtually impossible for socialists to get a hearing within those institutions. If our discourse were proceeding rationally, Bernie’s continued performance against Trump — even after his opponents dropped the “hasn’t been vetted” line — would be rightly understood as an existential challenge to liberal hegemony. That it isn’t understood this way, and remains largely downplayed or ignored by Democratic party loyalists, says everything one needs to know about how rational this discourse actually is.