And if interviews with about a dozen Sanders supporters who gathered here this weekend are any indication, the “Bernie or Bust” component of his large following will survive past the summer, even if Mr. Sanders eventually endorses Mrs. Clinton.

“He’s been fighting against the 1 percent, and Hillary has become the 1 percent,” said Mr. Winnett, an unemployed computer engineer. “She’s become everything that we’re against.”

Mr. Sanders has yet to concede the nomination, though in a speech streamed live last week to more than 200,000 viewers, he hinted that he might endorse Mrs. Clinton, saying, “The major political task that we face in the next five months is to make certain that Donald Trump is defeated and defeated badly.”

Mr. Sanders’s advisers say that before he throws his support behind Mrs. Clinton, he is seeking assurances that she and the Democratic Party will embrace some of his ideas. Much of his speech was devoted to urging his followers to continue fighting for causes like universal health care, free public college and an end to fracking, regardless of who wins the general election in November.

That happened to be the theme of the gathering this weekend, which was called “The People’s Summit” and drew thousands of people to McCormick Place, a large conference center in Chicago. Against a backdrop of Twister games, Lego sculptures and beanbag throwing contests, they talked about pushing progressive ideals.