The Sanders’s instincts served them well, at least in terms of how the spot would be received by his supporters: A blast email on the day of his announcement with the text from the do-it-yourself ad drew an enthusiastic response. Even though there was no direct fund-raising request in the ad, it helped Mr. Sanders raise a record $6 million in the first day of his campaign.

But it marked a humiliation for his consultants, who quit after concluding that Mr. Sanders was not willing to empower them.

It is not clear how much Mr. Sanders will ultimately bend to the wishes of his current advisers. But his new team sees enormous opportunity in his twin rallies this weekend — platforms to showcase big, diverse crowds of supporters, which could address questions that have dogged him since 2016 about his appeal to nonwhites.

And though his rally in Brooklyn will be something of a homecoming, it is also a chance for him to make an aggressive play for young, white urbanites at the same time that another one of their favorites, Beto O’Rourke, is expected to enter the race.

Even so much as acknowledging his biography would be a change for a senator who has long rejected sharing anything about his life. But his advisers are betting it could help set him apart from a crowded field of candidates, many of whom support the same policies that had made him unique in 2016.

At his Brooklyn rally, Mr. Sanders is expected to at least nod to the years when he played stickball in the street and arguments between his parents over money were commonplace. In Chicago, his advisers hope he will talk about his civil rights activism there, including how he was arrested during a protest on the South Side.

But above all, the rallies will test just how much Mr. Sanders, whose message has largely remained the same throughout his political career, is willing to evolve, if at all. Those closest to the senator acknowledge that he is unlikely to change, even as he recognizes the importance of sharing his personal story.