Pundits, myself included, made the mistake of declaring former vice president Joe Biden politically dead and Senator Bernie Sanders the 2020 Democratic front-runner after only three presidential nominating contests in February. Just a week later, many repeated the mistake in reverse, writing off Sanders after Biden surged back with a landslide win in South Carolina, then took 10 of the 14 states on Super Tuesday three days later.

Fact-check: Biden was never dead—and Sanders wasn’t, either, after Super Tuesday. But combined with his losses the next week in Mississippi, Missouri, and especially Michigan, the bad Super Tuesday news uncovered the main lesson that, if not heeded, could ultimately doom his campaign: Black voters matter, and despite running a better, more diverse campaign than he did in 2016, Sanders is overwhelmingly losing them.

If I could point to one big mistake Sanders made in those few crazy days when the script flipped, it was this: He departed South Carolina the day before its primary to head to Boston for a rally and skipped going to Selma, Alabama, the next day to honor the 55th anniversary of the Bloody Sunday march demanding voting rights for African Americans.

What did that look like to voters not sold on him and his political revolution? It looked as though Sanders disrespected the voters of South Carolina (where he came in second out of seven candidates—not too shabby) by leaving early and not thanking his supporters after results came in. He went to Massachusetts, where only days before, he and Senator Elizabeth Warren were neck and neck. He managed to edge her out there, but Biden beat them both, easily. (And what did Warren supporters see? Sanders making sure he could deny her a win in her home state.) Meanwhile, Sanders insulted the black voters of Alabama, a Super Tuesday state, by skipping the annual pilgrimage to Selma, a civil rights holy day.

Anyone who wants to know why Sanders overwhelmingly lost the black vote in South Carolina and the six Southern Super Tuesday states—or why suburban white women, who won the House of Representatives for the Democrats in 2018, moved to Biden at the same time—should look at those choices. It’s why Sanders lost Mississippi by an astonishing 65 percentage points on March 10 and why Biden won Missouri and Michigan. If Sanders wants the Democratic nomination, he’s got to correct course with both groups.

Before all that, Sanders made an even bigger mistake. He never asked House majority whip Jim Clyburn of South Carolina, who backed Biden three days before the primary, for his support. ”His politics are not my politics,” Sanders told MSNBC’s Rachel Maddow the night after Super Tuesday. “And I respect him, but there’s no way in God’s earth he was going to be endorsing me.”

Maybe not, but how hard would it be to make a courtesy call to Clyburn? He’s a very nice guy. He lost his wife six months ago—and Biden, a man of so many losses, reached out to him. Sanders learned in 2016 that the road to the Democratic nomination ran through South Carolina and through Clyburn, who endorsed Clinton four years ago. If you sat down with him and made the ask, however futile, at least you could say you tried. And in the South and in politics, polite gestures like trying go a long way.

Nevertheless, when Biden crushed Sanders in the Palmetto State, I resisted the conclusion I drew when Clinton did the same thing in 2016: that the Clyburn-endorsed Democrat would destroy Sanders in the Southern states to come. In 2020, Sanders had some great black organizers on the ground in all those states, to his credit. His campaign went out of its way to add local staff, mainly young people of color.

But Biden won the Southern Super Tuesday states. Exit polls say he won roughly the same share of black voters that he won in South Carolina and that Sanders won essentially the same small percentage he had across the region in 2016. In Alabama, North Carolina, Oklahoma, Tennessee, Texas, and Virginia, according to exit polls, Sanders averaged 18 percent of the black vote—not much more than he got against Clinton in 2016—while Biden had roughly 60 percent, in a five-person race. (Representative Tulsi Gabbard was also on the ballot, but she won only two delegates, in American Samoa.)

Yet in the wake of Super Tuesday, Sanders didn’t face the fact, at least publicly, that he’s still got problems with black voters. After South Carolina, Sanders surrogate Michael Moore went on MSNBC to claim the state “is not representative of the United States.” Sanders could have rebuked Moore but didn’t. Online, Sanders’s supporters took to calling them low-information voters, which happened in 2016 as well. Again, no rebuke. Instead, Sanders railed against “the establishment” coming together to back Biden. It did—but that’s not why he lost black voters. Former South Bend mayor Pete Buttigieg and Minnesota Senator Amy Klobuchar dropped out and endorsed Biden because they saw they had zero traction with black voters and could never win the Democratic nomination. They certainly didn’t bring African Americans over to Biden’s column.

But when Maddow asked Sanders why he’s not winning with black voters (except, to be fair, the younger ones, according to some polls), he quickly changed the subject. “Let me give you the other side of the story,” he said. “In California, if my memory is correct, we received 39 percent of the votes of people of color, which were Latinos, Asian Americans, and African Americans.” Sanders has made remarkable inroads with Latinos, particularly in California and Nevada. According to The New York Times’ preliminary California exit polls, he won 55 percent of Latinos and a plurality (37 percent) of Asian Americans. But he lost the black vote there to Biden, who won 38 percent, and to former New York mayor Mike Bloomberg, who got 20 percent. (Sanders won only 18 percent.) Likewise in Nevada, he won the Latino vote handily but lost African Americans to Biden. You can’t elide black voters to make the electoral math easier; there’s no way around Sanders’s problems with black voters except through them. And he should have learned that four years ago.

Then there’s the other component of Biden’s Super Tuesday wins: the white, college-educated suburban women who helped Democrats recapture the House in 2018. It turns out that Democratic primary turnout has surged since 2016, but it’s mainly among moderates, like those white, college-​educated suburban women, not the young people Sanders counted on. Those female voters, along with black voters, powered Biden’s overwhelming win in Virginia, where the state legislature has flipped blue, thanks to an increase in the number of women candidates and voters, as well as his surprise victory in Texas, where he carried the suburbs around Dallas and Houston that also went blue in 2018—again on the strength of suburban women.

Those women don’t factor heavily—or at all, actually—in Sanders’s political rhetoric. But they do factor heavily in the rhetoric of some of his online supporters, many of whom deride them as wine moms and the middle-aged hysterics who make up the resistance (and worse). Here’s the thing: Those “wine moms” and “middle-aged hysterics,” along with “low information” black voters, are the base of the post-Trump Democratic Party that Sanders wants to lead. And if he doesn’t have a strategy for winning them, he’ll lose again.

Prominent voices in the Sanders left spent most of their not-so-super Wednesday—let’s call it Shitty Wednesday—deriding those voters while calling for Warren to drop out. Let me say this about Warren, who was by far the candidate most qualified to be president and who did drop out, on Tragic Thursday: She took it from the left, right, and center, while the media virtually erased her.

Now that Bloomberg’s campaign is in the rearview mirror, we can see that it was mainly targeted at Warren. Bloomberg supported Biden but didn’t think he could win. He spitballed Sanders but didn’t appear to believe he could win, either. Meanwhile, he trashed Warren before he even got in the race, calling her wealth tax “Venezuelan,” and rapped her disrespectfully just before he got out. When a reporter asked about her on Super Tuesday, he answered derisively, “I didn’t realize she was still in. Is she?” Whoever wins the Democratic nomination will owe Warren big for taking Bloomberg out in his first debate. I celebrate that she outlasted him, if only by a day.

To the extent there is a Democratic establishment, it came for Warren, too. When it looked as if Biden had a little bit of life, not just Buttigieg and Klobuchar but also dozens of congressional leaders and state representatives flocked to Biden—as did former Senate majority leader Harry Reid, who helped coax Warren into running for the Senate in 2012 and is widely known to admire her. You might have imagined liberal establishment Democrats seeing an accomplished, progressive woman as a better foil for Sanders than the crime-bill-sponsoring, bank-defending former senator from Delaware, the credit card capital. But you’d have imagined wrong.

And of course, the attacks came from the left. Warren made the mistake of believing that all those people who chanted “Run, Warren, run” in 2015 and 2016 would follow her in 2020. Instead, a critical mass went with Sanders. And instead of viewing her as an ally whose support they might need in the event her candidacy faltered, many Sanders supporters treated her as the enemy. They spread ugly rumors that she lied about losing her first teaching job because she was pregnant. They trashed her Medicare for All plan. When health care advocate Ady Barkan, who has ALS, backed Warren over Sanders last year, he was savaged by Bernie supporters who alleged that the disease claiming his body had taken his mind. (To his credit, Sanders defended Barkan.)

When Warren told her truth, the way she remembered it, about Sanders expressing doubt that a woman could win the White House, he effectively called her a liar on national television, and his supporters drowned her in snake emojis.

Even if suburban “wine moms” and “resistance hysterics” didn’t cast their votes for Warren, they saw all that first. And it continued as Sanders backers demanded she drop out, with Representative Ilhan Omar suggesting Sanders lost her home state of Minnesota because of Warren’s continued campaign. (I might think more about what I could have done to bring in my home state for Bernie, but that’s just me.)

So Warren dropped out, crushing every woman who hoped that this year, with the range of qualified women running, we might finally end up with a woman in the White House. I’m sad, but Sanders’s supporters should be sad, too. I wrote this, repeatedly, four years ago, and it’s still true, but I’ll let Sanders-sympathetic New York writer Eric Levitz say it instead: “Median Democratic primary voters like the Democratic Party and its leadership.” Or as The Root’s Michael Harriot put it in a tweetstorm, “All we have is the institutions, organizations and relationships we built. That’s why politicians come to black churches in the south. That’s why a lot of activists down here are also educators and religious leaders. It’s why Dem. Party meetings take place in church basements. That is quite literally ‘the establishment’ for us.”

If Sanders wants to lead the party, he’s got to start reaching out more to its core constituencies—and he’s got to get his supporters to stop savaging those constituencies. As Representative Alexandria Ocasio-Cortez tweeted, “Effective organizers are welcomers, natural educators, and positive in their interactions. They make new people feel like theirs is a movement they want to be part of.” Despite her close ties to the Sanders campaign, she was obviously subtweeting his supporters, who were demanding Warren’s backing as if it were their birthright.

The browbeating didn’t work. Warren dropped out without endorsing Sanders, and in an interview with Maddow the same night, Warren criticized him for failing to rein in his nastiest supporters. “Bernie and I have been friends for a long, long time,” she began, before denouncing some of the worst instances of his supporters’ misbehavior, including threats and other abuse faced by leaders of the Working Families Party, which supported her, and Nevada’s Unite Here union, which criticized Sanders’s (and Warren’s) Medicare for All plans, only to find its female leaders’ phone numbers and addresses leaked online. “It put them in fear,” Warren said. When Maddow asked if it was Sanders’s responsibility to stop such abuse, Warren said simply, “It is. It just is.” It’s possible that by the time you read this, she will have endorsed Sanders. But listening to her on Maddow’s show, it didn’t seem that would happen anytime soon.

Sanders continues to represent a movement that at its best promises to transform our democracy as well as create a fundamentally fairer, more humane society. But to make it a majority, not just a movement, he and his advisers need to study the lessons of South Carolina and Super Tuesday. He must reckon with the doubts of black voters, who are the party’s most loyal supporters. As he moves into the later-voting states, never again should he pass up the chance to confer with party elders like Clyburn. Even supporters agree. “We need to sit down with as many Congressional Black Caucus members as we can, whether they endorsed us or not,” Representative Ro Khanna, a Sanders campaign cochair, told Politico. Sanders must make inroads with suburban women rather than let his loudest backers write them off as insufficiently radical to deserve his movement’s attention.

In the end, a primary race some thought might last through the July convention could be over in March. Biden remains a vulnerable candidate, both on the issues and in terms of his behavior on the campaign trail. But Sanders dug himself a hole. To get out of it, he’ll need to sound as if he wants to be the leader of the party whose nomination he seeks, not its destroyer.