Last week, in the days leading up to Sanders’ withdrawal and after, the two spoke several times — including Wednesday, when the Vermont senator formally suspended his campaign. Sanders and Biden’s teams have also been in regular communication, with Sanders’ campaign manager Faiz Shakir and senior adviser Jeff Weaver speaking with Biden’s top two advisers, Anita Dunn and Ron Klain.

Sanders’ endorsement was no mere formality. Though the Vermont senator formally suspended his campaign last week, Sanders did not say he endorsed Biden, nor did he call on his dedicated followers to vote for his former opponent. Sanders also pledged to hang on to his delegates, which caused some Democrats to fear the primary could wind up repeating the mistakes of 2016, when acrimony marked the relationship between Sanders and Hillary Clinton in 2016. Many Democrats believe that bitter divide played a role in her loss to Trump in November.

That rancor between Clinton and Sanders surfaced again this year when the former senator and secretary of state made headlines during the primary for saying “nobody” likes Sanders.

But Biden did. He always made sure to be friendly and respectful with Sanders, who repaid the favor — sometimes too much, Sanders advisers fretted when he refused to bludgeon Biden on the debate stage.

Even in 2016, Sanders aides note, Biden made sure to praise Sanders when he was anathema to the rest of the Democratic establishment.

"Bernie is speaking to a yearning that is deep and real. And he has credibility on it. And that is the absolutely enormous concentration of wealth in a small group of people with the middle class being left out,” said Biden in January 2016. "It's relatively new for Hillary to talk about that.”

Biden repeated those words about Bernie’s credibility as he lavished praise on his former rival Monday.

Sanders’ endorsement gave Biden a chance to break into the news cycle with a headline-grabbing announcement, a rarity in recent weeks as he, along with Sanders, remains stuck at home during the pandemic as reports about the contagion and the president’s response to it suck up all the media oxygen.