When Bernie Sanders hung up his presidential bid at the Democratic National Convention last year, progressive thinkers were grappling with a critical question: Could the enthusiasm Sanders had generated be replicated outside a presidential campaign?

Sanders had already jolted Democratic leaders, proving there was a massive audience for policies that were once laughed off inside the Beltway. He’d upended the political fundraising model with his online small-dollar donation strategy. But he lost. And according to everyone in Washington, Democrats only really mobilize in presidential elections.

On Sunday, the independent senator from Vermont will again begin attempting to counter the conventional wisdom. Across the country, Democratic politicians are holding at least 40 rallies intended to strengthen public resistance to a new wave of Republican attacks on Obamacare and Medicare ― and hear from voters about their concerns.

“For the first time in the modern history of the Democratic party, we’re going to see aggressive outreach efforts,” Sanders told The Huffington Post. “This is a beginning, I hope, of a transformation in the Democratic Party. … Our work has to focus on energizing people where they live and showing them what we are fighting for.”

Sanders rallies in 2016 were part economics lecture, part religious revival. They built a deeply committed group of supporters, but for many, their loyalty was to Sanders himself, not the Democratic Party. After Hillary Clinton’s loss to Donald Trump, there are huge numbers of Sanders supporters more comfortable with saying “I told you so” (and to be fair, they did) than helping the Democratic Party get back on its feet.

Sanders wants to bring them into the fold. But he can’t do 40 rallies across the country in a day. Mayors, governors, state senators and other Democratic leaders will be on stage at other rallies. To make the wave of events a reality, Sanders had to win over new allies in the Democratic establishment.

Senate Minority Leader Chuck Schumer (D-N.Y.) didn’t miss the Sanders campaign and is fully aware of the economic issues that factored into Trump’s presidential win. He’s been using the term “populism” approvingly on Capitol Hill, and on Sunday, he’ll join Sanders at a rally in Warren, Michigan.

“The Democratic Party is only as strong as our grassroots,” Schumer told HuffPost. “If we’re going to stop Republicans from rolling back the progress we’ve made and if we’re going to advance policies that help the middle class and those struggling to get there, we need to harness the energy outside of Washington, D.C.”

A decade ago, Schumer and Sanders would have made unlikely allies. Schumer has several Wall Street-friendly votes on his record, and outrage over the bank bailouts was a critical fuel for Sanders’ 2016 campaign. But the rallies on Sunday demonstrate that both Sanders’ policy vision and his preferred political tactics are moving into the Democratic mainstream.

What, after all, do Democratic leaders have to lose? Since President Barack Obama took office, the party has lost over 900 state legislature seats, while ceding 12 governorships, the presidency and control of both chambers of Congress. Absent a man named Barack Obama at the top of the ticket, the party doesn’t win at the federal level. And even with Obama in charge, the states have been a disaster.

The party strategy of the last 30 years has been to ignore most rural areas, while trying to run up the score in presidential elections by targeting big cities with TV ads. Most voters live in big cities, and a lot of Democratic policies benefit urbanites. But they didn’t turn out in 2016. And populist policies have a lot to offer other communities the party has traditionally ignored. There’s a reason why populism is, you know, popular.

But winning those voters ― both urban and rural ― requires active engagement, not the passive satisfaction of agreeing with a commercial.

“We have to connect with voters,” Sanders said. “Not just through an inside-the-Beltway strategy, but through aggressive grassroots outreach where we don’t just talk on TV, we go out and we talk to people in their communities.”

On the 2016 campaign trail, Sanders was on offense, promising a vision of a better future with universal health care, free college tuition and a $15 minimum wage. With Trump as president and Republican majorities in both chambers of Congress, there aren’t many areas for Democrats to make new gains at the federal level. As Sanders knows, it’s hard to inspire people with a celebration of the status quo. Still, he hopes to make the most of a defensive pitch.

“The goal of those rallies is to make it clear to the Republican Party … that they’re not gonna throw 30 million people off of health insurance. That they’re not gonna decimate Medicaid … that you’re not gonna privatize Medicare and turn it into a voucher program. You’re not gonna cut health care so you can give tax breaks for the wealthiest Americans.”

Correction: This article initially stated the rallies are scheduled for Saturday. They are on Sunday. It also referred to Chuck Schumer as the Senate Majority Leader. He is the Senate Minority Leader.