Nancy Pelosi had thrown cold water on calls for impeachment for more than two years. As Donald Trump used the presidency to enrich himself and his family; as he separated migrant children from their parents and locked them in cages; and especially as the Mueller investigation unfolded, the Speaker of the House counseled caution. Pelosi based that strategy on two pillars: a belief that her party’s nominee has a good shot at beating Trump in 2020, and the need to protect congressional Democrats who are vulnerable to defeat in swing districts.

There’s been a third, underappreciated factor in the Pelosi impeachment dynamic: money. The California congresswoman is tightly focused on adding to her House majority next year, an effort that will require tens of millions of dollars. And major donors to the Democratic Congressional Campaign Committee and the House Majority PAC have been in alignment with Pelosi’s go-slow approach. “It’s people in the financial industry and tech and real estate who are bundling and maxing out in their own right, but also giving to Pelosi’s vehicles, so they have a disproportionate impact,” a well-connected Democratic operative says. “For example, Sean Parker or Jim Simons, who is a billionaire, and one of the biggest donors to the Democratic Party, and one of the most important donors to Pelosi’s super PAC.”

Certainly there are plenty of Democratic fat cats, including Tom Steyer, who have been aggressively advocating for impeachment, and would have been thrilled to see Pelosi act sooner. Yet even the influence of big money became irrelevant in the past week as Pelosi’s position crumbled.

Pelosi’s dramatic reversal is not only the result of a new outrage and changed minds. It’s also evidence of a larger shift in the balance of power in Democratic circles. Clearly a whistleblower coming forward to call attention to Trump’s alleged shakedown of Ukraine was brave and pivotal. Then, as damning leaks about Trump’s conduct continued to appear, a wave of House moderates—the people Pelosi claimed to be protecting—declared they were now in favor of impeachment. But the fast-moving events of recent days would not have been possible if grassroots activist groups had not consistently applied pressure after the seemingly disappointing results of the Mueller report. When “frontline” congressional members went home over the summer, they were besieged by constituents in favor of impeachment.

“You couldn’t have gone from 0 to 60 miles per hour just based on Ukraine,” says Brian Fallon, who was a top campaign aide to Hillary Clinton in 2016. “But roughly 150 members had already come out for impeachment before Ukraine. If groups like MoveOn and Indivisible hadn’t built that foundation, you’d be starting from scratch trying to get freshmen from swing districts, and it would have been much harder. Then over the weekend, the Pod Save America guys, who are still sort of party establishment types, really went after Pelosi, and I’m sure that got her attention.”

Big money remains the dominant force in national politics. But Pelosi’s move to finally launch an “impeachment inquiry” is a loud demonstration of how times have changed. “She’s had a year to show us anything resembling a playbook for going on offense against Trump, and she’s been in a crouch,” the progressive Democratic operative says. “If this was 2006, she could have stayed there, insulated. But the netroots movement grew from that frustration with the unresponsive Democratic majority leadership after Bush, and now the scream from the base has overwhelmed any tactical leadership Pelosi has attempted.”