In the right circumstances, the South Carolina primary, the first with a significant number of black voters, can have an enormous influence on the Democratic presidential nominating contest. That’s what happened in 2008, when then-Sen. Barack Obama finally moved ahead of former secretary of state Hillary Clinton in polls after a decisive win there, and went on to capture the nomination.

This year, we’re told it’s a “firewall” for Joe Biden, who could sure use one. And he just got a piece of welcome news, as Rep. Jim Clyburn, the most important Democrat in the state and the highest-ranking black Democrat in the House, is reportedly going to endorse Biden this week, in advance of Saturday’s primary.

As Politico reports, some Democrats see this “as a last-ditch effort to blunt Bernie Sanders’ momentum before he runs away with the nomination.”

So how much can it help?

While there is some evidence from political science that endorsements can have a positive effect, every endorsement communicates something slightly different. For instance, when Sen. Edward M. Kennedy endorsed Obama, it was a validation of his momentum and a sign that significant portions of the party were swinging away from Clinton and toward him. But it came just after Obama won that victory in South Carolina, and there isn’t much evidence that other than creating a good news day or two it actually changed many votes.

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The whole idea of an endorsement is that as a voter you’re outsourcing your judgment of a candidate — at least to some degree — to someone else you’re more familiar with. I might not know much about this guy running for Congress, but gun rights are important to me, and if the NRA endorsed him, that’s all I need to know. I trust my hometown paper and they say this candidate is thoughtful and principled, so I’ll take their word for it. And so on.

But in a presidential race, voters are working with comparatively more information. In this case, Biden is a particularly well-known figure after having been vice president for eight years. If you’re a South Carolina Democrat, you probably don’t need to rely on Clyburn to tell you what to think of him.

On the other hand, maybe you do. Right now, there are millions of Democrats who are being pushed and pulled by all kinds of contradictory feelings about their party’s presidential candidates, both logical and emotional. Black voters have been the foundation of Biden’s support, which you can explain in multiple ways, including residual good will from his service for Obama and a practical assessment that an older white candidate is needed to beat President Trump. (After 2016, it seemed that black Americans were among the only ones who weren’t surprised that the country would elect an unapologetic bigot.)

The trouble with “electability,” however, is that you only look electable until you don’t. That discussion has been particularly hard on Biden, who was the consensus “electable” choice for a while, but has recently dropped in the polls and doesn’t seem so electable anymore.

I’d argue that the revised impression of him is the more accurate one. Biden may have appeared electable because of his résumé or his more moderate positions, but he was always less electable than many people realized, for the simple reason that he’s terrible at running for president, which he’s now demonstrating for the third time.

There’s another reason why Clyburn’s endorsement may not help Biden much, for all the respect he commands: It’s no surprise to anyone. As a member of the House leadership and a congressman for over a quarter-century, Clyburn is the ultimate establishment figure. If he was going to endorse anyone, it would almost certainly have been Biden.

So if you’re a South Carolinian trying to make your decision, his endorsement may make you feel a touch warmer toward Biden, but it doesn’t tell you anything you don’t already know.

Fairly or not, South Carolina could determine Biden’s fate in this nominating contest. If Biden wins there you’ll see a hundred “Comeback kid!” articles. If he doesn’t, the media will pounce to declare his candidacy over.

And once they’ve done that, there’s almost no coming back, no matter who might endorse him next.

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