It's from The Atlantic. Basically before Sanders' dropped out he was invited to talk with Biden's campaign. From that same article

But over the past year or so, McElwee seems to have reassessed his position in the left-wing firmament. He no longer talks about eliminating Immigration and Customs Enforcement. Instead, he’s become an evangelist of political persuasion and coalition-building. He’s become much more openly critical of his progressive compatriots. And most shocking to some of those compatriots, he’s advised the Biden campaign.

“I’ve come to the realization that the Democratic Party is actually ripe for a transformation into a progressive vehicle,” McElwee told me. Progressives should be working to build power and influence within the party, district by district and voter by voter—not to overthrow it. “We have lost this muscle of persuasion,” he said.

In their March meeting, McElwee and a colleague attempted to persuade the Biden team to endorse a kind of quasi–Green New Deal. Their hope: If the presumptive Democratic nominee took a stronger stance on climate change in particular, he could get more young people and progressives excited about his campaign. They urged the campaign to endorse a commitment to reaching net-zero emissions by mid-century, and to invest in low-income communities that are disproportionately affected by pollution. The Biden team was worried that moving left on climate would be all risk and no reward. But McElwee assured them that it would be both popular and good policy. They didn’t extract much in the way of immediate commitments, McElwee told me after the meeting. But he had—he has—a longer-term plan.