Mr. Sanders, who in 2016 accused the Democratic establishment of conspiring to support Mrs. Clinton, took note of all these moves, but he has made no such charges against Mr. Obama.
In fact, one of his campaign advisers, speaking on the condition of anonymity in the wake of last month’s string of Sanders defeats, said the senator was grateful for Mr. Obama’s neutrality throughout the campaign. And Mr. Sanders, who has denied reports that he contemplated a primary challenge to Mr. Obama in 2012, had made a point of reaching out to the former president several times in recent months to update him on the progress of his campaign.
Before those conversations, the two men had a polite but frosty relationship, and some of their private exchanges over the years devolved into policy debates, former aides said. But Mr. Obama saw Mr. Sanders’s overture as an opening to assume the peacemaker’s role he believed himself best suited to play.
Since leaving office, Mr. Obama has ruminated about what he could have done differently, both as president and as a campaign surrogate for Mrs. Clinton, to stop Mr. Trump’s ascent, and concluded that he needed to do more to repair the damage from party infighting.
“His true north is winning back the White House, period,” said Valerie Jarrett, a close friend and adviser to the former president, in a phone interview last month. Mr. Obama, she added, would “have backed any nominee, any of them, with the same conviction.”
Mr. Sanders is much closer personally to Mr. Biden despite their political differences, but Mr. Obama, unlike Mr. Biden, remains a trusted figure to many Sanders supporters, so much so that his campaign released an ad that featured a patchwork of clips with Mr. Obama lavishing praise on Mr. Sanders.
In the end, Mr. Sanders concluded that negotiating a détente through the former president would ease the blow of his withdrawal on his base. Whether Mr. Obama’s involvement will ultimately draw Sanders voters to support Mr. Biden’s candidacy remains an open question, and some supporters, including Mr. Sanders’s own campaign press secretary, say they won’t.