Despite its growing ranks, the progressive caucus has struggled for years to enact its agenda of providing more robust health care services, taxing the wealthy, reining in military spending and addressing climate change. Activists have grown frustrated as they helped elect members to Congress, who then fell in line, voting for whatever Democratic leaders put on the floor.

In recent years, the caucus has tried and failed to cut military spending by 10 percent and struggled to enact major tenets of what it calls its People’s Budget. High-profile progressives protested this year over a lapsing eviction moratorium. But the effort failed to muster enough support for Democratic leaders to put legislation on the floor to extend it.

This week’s machinations buoyed the movement. During a private meeting of the progressives on Friday evening, lawmakers were celebratory as they discussed how they were able to “hold the line” for Mr. Biden’s agenda.

“It’s undeniable that this is a new era of progressive power,” said Mary Small, the national policy director of the Indivisible Project, a grass-roots group. “They had a list of what their priorities would be for the reconciliation bill, and they’ve been dogged.”