More than 25 grass-roots groups signed on to lobby together for campaign-finance reform, single-payer health insurance, more aid for public schools, a ban on fracking and other goals, said leaders of the New York Progressive Action Network, the name of the coalition.

Several coalition leaders said they decided in July at the Democratic National Convention that they should band together to keep fighting income inequality, a hallmark of Mr. Sanders’s campaign.

“It’s not about him,” said Kelleigh McKenzie, a member of Ulster Progressive Action. “It was never really about him. It was about the principles.”