“Our job isn’t to be nice,” said Alexandra Rojas, the executive director of Justice Democrats, the progressive group that has roiled Washington by challenging more centrist congressional Democrats from the left.

“Our job is to say that the planet is literally burning and is going to be uninhabitable within our lifetime and that it’s not just Republicans who are the easy boogeymen — it’s Democrats, too, that have set in this mentality that we can wait,” she said. “The battle for the soul of America is happening right now and at every point in history, it’s never been popular but we have to do it.”

Karine Jean-Pierre, the chief public affairs officer at MoveOn.Org, said the run-up to the Iowa caucuses would be a critical window for liberals, who must build further public support for their causes to hold candidates responsible.

“We now need to use these ideas to mobilize the base,” she said. “It’s really about how can we use these ideas to win in 2020, and we use the primaries to give people a vision of what a Democratic president would look like.”