He and Warren are ideological allies who have developed a good working relationship—not friends, but warmer with each other than most senators are. He respects her, thinks she gets it, despite the distinctions she’s recently made to point out that she, unlike the Democratic socialist from Vermont, is “a capitalist.” Sanders invited her to appear at a few events he hosted. They did some web videos together. Showdowns were avoided, like when Sanders declined to endorse his old ally Dennis Kucinich in the Democratic primary for Ohio governor earlier this year because it would have put him at odds with Warren, who had immediately backed her protégé Richard Cordray in the race.

Warren is close to pulling the trigger on a run, and has spent the past two years putting together the pieces for a campaign, accelerating since the end of the summer. This included some deliberate overtures to Sanders’s world, like reaching out to Nina Turner, the former Ohio state senator who now runs the Sanders-inspired group Our Revolution, and to RoseAnn DeMoro, the former head of National Nurses United, which spent millions and went all out for Sanders in 2016.

The Warren analysis is that Sanders’s votes in 2016 had more to do with being the alternative to Hillary Clinton than he likes to admit. For all his strength then, he’s not leading in early public polls, which show him with support in the teens, not far ahead of Warren and behind Joe Biden. She’s a woman at a time when women are proving key to the party’s future. She has an appeal beyond just his supporters, drawing from many Clinton supporters, too.

“The whole thing that they have the same core of support tends to be overstated,” said a Warren ally.

Her moves were never about pushing Sanders out of the way, but about pushing forward on her own.

Strategically, Warren started carrying out clear moves to show her seriousness, from making a tactical decision to say a few weeks ago that she would take a “hard look at running” after the midterms, to arranging a Washington Post story last Sunday that showed off the inner workings of her political operation, paired with a rollout in The Boston Globe and on Twitter on the Cherokee question.

“He’s not the kind of guy that you intimidate out of something,” the Sanders adviser Mark Longabaugh said.

For a long time, it didn’t seem like things were going to go down this way.

At a presentation to Sanders and his inner circle in January, Longabaugh identified Warren as the main obstacle to winning the nomination. Though others at that planning session disagreed with how big of a threat she posed, they were still hoping to avoid it. A rough idea emerged among them of how it would play out: At some point around now—right before or right after the midterms—the two senators would have a conversation. Sanders would tell her what he had decided to do. If he was a go for 2020, he’d expect her to support him, for the sake of the cause. If he decided not to run, it would essentially be permission for her to go ahead, though likely not with his endorsement right away.