Sen. Bernie Sanders, D-Vt., may have sought to defuse his feud with Rep. Alexandria Ocasio-Cortez, D-N.Y., by announcing an endorsement of her super PAC, Our Revolution. But that is only a very small step toward healing the wounds of a feud that erupted after a notorious primary campaign appearance last week. The real work of rehabilitating Ocasio-Cortez and putting an end to the bickering will need to happen if Sen. Sanders is to take his rightful place in a critical Democratic presidential primary in 2020.

Mrs. Ocasio-Cortez had called for Sanders to resign from the Senate over allegations that he had engaged in sexual harassment. Sanders used his position as a champion of the movement to defend himself, blaming the fundraising skills of the federal government and demanding that the alleged harasser quit his job.

Sanders proceeded to mock Ocasio-Cortez as a liberal talking point: “I’m not sure what the significance is of the article written by a reporter with The Intercept.” He retweeted rumors that the disgraced staffer had been fired, and asked his followers if they believed it.

Despite the heft of the insults, the nation’s leading progressive party institution, the Democratic Socialists of America, spoke in Ocasio-Cortez’s defense. “His treatment of some employees at the Sanders presidential campaign that many accused him of sexual harassment, certainly he should apologize,” the DSA said.

Sanders’ leadership of the DSA led other progressive activists, including Fight for $15, to distance themselves from the lefty group and condemn Sanders’ leadership. “That report has no basis in fact,” said an official with Fight for $15, referring to the Daily Beast report that Sanders and some of his top aides had tried to cover up claims of sexual harassment.

So what’s the deal? Why does Sanders keep going down the road of insulting and humiliating the woman who could dethrone him in the party, and its likely presidential nominee in 2020?

It’s easier to defend Bernie Sanders if you live in a cocoon of progressive dogma. In fact, as always in politics, Sanders has proven to be unapologetically progressive and he is still polling among the top Democratic presidential candidates. A survey last November showed Sanders ahead of other leading Democrats, including Sen. Elizabeth Warren, D-Mass., in the case of Democrats who favor single-payer health care.

But for progressives who might ordinarily lean toward Ocasio-Cortez, the distasteful firefight reinforces a belief that Sanders has ignored them and insists on ignoring his critics in the party. It does them no favors. Sanders cannot sit back and let the primary showdown rage on when his own supporters do not even share his fervor for single-payer health care. The senator can only benefit from engaging all parties to the discussion and positioning himself in a bigger role in the party.

He has to renounce the language that his critics have seized upon and condemn Ocasio-Cortez and her allies. He cannot speak ill of her.

Sanders’ complaint that he needed to spend a considerable amount of money and time campaigning in the U.S. Virgin Islands for another candidate in order to investigate the sexual harassment allegations was just laughable.

And he should have acted quickly to heal the rift with Ocasio-Cortez and finish the formal endorsement that the social justice group, Our Revolution, needed.

Sanders and Ocasio-Cortez are peas in a pod — basically, liberal Democrats by every standard but also progressive activists, who support single-payer health care and deregulating the economy. This can only serve to discredit the Sanders brand and give credibility to AOC’s accusations. The pair have shown a measure of unity in opposing his calls for federal income taxes for the rich and other tax hikes.

Sanders has all the celebrity and political skill to occupy a prominent role in the presidential primaries. But at the moment, he seems to be locked in a contest with Democratic voters who haven’t given him much support.

Sanders’ problem has much to do with his inability to seem like he understands that and speaks for all of them. The real damage done to Sanders will only be repaired if he sticks around and unites his fellow Democrats.