A group of people hold up signs during a meeting held by the American Civil Liberties Union on Saturday in Coral Gables, Fla. (Luis M. Alvarez/Associated Press)

It had all the trappings of a campaign rally: the signs, the Bruce Springsteen songs on repeat, the clipboard-hugging volunteers in matching T-shirts.

But the 2,000-odd people in the University of Miami’s basketball arena were there to hear Anthony Romero, the executive director of the American Civil Liberties Union, try to recruit them into a legal army.

“It didn’t take a lot of work to fill this auditorium,” Romero said, as the screens surrounding him showed mass protests against President Trump. “People want to be deployed. They don’t just want to write you a check, or sign a petition. They want to be engaged. You want to be protagonists with us.”

The ACLU is spending millions of dollars on a plunge into grass-roots politics — a “People Power” campaign. It’s the newest and largest development from a sprawling “resistance” movement that regularly moves faster than the Democratic Party’s leaders can think and isn’t waiting on politicians for cues.

[ACLU is launching ‘People Power’ project to resist Trump policies in cities]

People Power debuted this weekend in South Florida and, by the organization’s estimate, at thousands of weekend house parties nationwide. Everyone who showed up received a nine-point plan to turn blue America into a network of “freedom cities” by defying the president’s executive orders, his health-care agenda and his Justice Department. Anyone who missed it could visit ­PeoplePower.org, the latest catchall website to find actions that would get results.

The key to the effort: targeting Trump’s policies, rather than the man or his words. If 2016 taught Democrats anything, it’s that attacking Trump isn’t enough.

“We’ve seen this exponential growth in people becoming card-carrying members of the ACLU,” Romero said in an interview after his speech. “They’re younger. They’re in every state around the country. The biggest danger was in not doing something like this, where people get apathetic and they fall asleep.”

There’s little apparent risk of that, and the biggest organizations on the left, broadly defined, are staffing up to give it direction. The Center for American Progress is planning a grass-roots conference for “rising” activist groups in California next month, and an ideas conference in Washington one month later. Super PACs such as American Priorities have become promotion machines for the Indivisible movement, which in just a few months has begun to organize some local chapters as official nonprofit groups.

But no organization is transforming as quickly or as boldly as the ACLU. Since the 2016 election, it has tripled its membership to more than 1.2 million and raised more than $80 million, with plans to add 100 staff members to a team of about 300.

[Keith Ellison, first Muslim congressman, calls for ‘mass rallies’ to stop Trump orders]

The donor and member surge was well underway on Inauguration Day, when Faiz Shakir, the ACLU’s new political director, showed up for his first meeting and pitched the People Power campaign. The people joining the ACLU, he said, were demanding that they act against Trump; here was a way to involve them in the process. Romero signed off on the multimillion-dollar plan immediately.

“If we’re going to have success fighting against the Trump agenda, my view was that it would come from the bottom up,” Shakir said in an interview. “The ACLU has a unique ability to reach people who aren’t dyed-in-the-wool blue, who don’t consider themselves progressive.”

Shakir was true blue, as were the people who’d make People Power work. Six of its key organizers, hired by Shakir, were veterans of the 2016 Democratic presidential campaign of Sen. Bernie Sanders (Vt.). According to Romero, Sanders’s digital veterans had shown how powerful a “decentralized agenda” could be for mobilizing people and getting them on the same page about a cause.

“The ACLU, especially at this critical time, is doing enormously important work,” Sanders told The Washington Post. “I congratulate them for stepping up to the challenges we’re all facing.”

And Shakir had spent seven years at the Center for American Progress, joining the office of House Minority Leader Nancy Pelosi (D-Calif.) in 2012 and moving to the office of Senate Majority Leader Harry M. Reid (D-Nev.) in 2013. From those perches, he’d seen what worked, and it was not a simple matter of instant political messaging. It was mobilization.

Over breakfast in Coral Gables, Shakir said that the National Rifle Association was one model for what the ACLU could do. “It used to be that the constitutional definition of gun rights was very limited,” he said. “They completely changed the law through their public advocacy. The Supreme Court has moved 180 degrees on a number of things because people moved them.”

Days into Shakir’s tenure at the ACLU, the group got its first test of how protest could move the law: Trump’s executive order banning entry to the United States by all refugees as well as people from seven mostly Muslim nations, and the protests and legal actions that sparked in the nation’s international airports.

“It was clear that mass mobilization really changed the way that judges viewed that,” Shakir said. “I saw that as the beginning. Mass mobilization has the ability not only to shape how judges see the law, but mayors, governors, school boards, sheriff departments.”

Miami-Dade County became an obvious place to test that. It was the only diverse, strongly Democratic area to comply with Trump’s order that threatened to cut funding to “sanctuary” cities and counties, places that selectively enforced immigration law and allowed undocumented immigrants to stay. In February, after a day-long community comment session, the county’s nonpartisan commission voted to affirm the decision.

Local activists weren’t sure how to stop it, but they adapted. The main South Florida chapter of Indivisible lobbied Broward County’s school board and passed a resolution stating that Immigration and Customs Enforcement could not enter the county’s schools without warrants.

That campaign brought them closer to the local ACLU, which was growing as fast as the national chapter. On Saturday, a few hours before the main People Power rally, more than 200 locals packed a Broward County library to hear legal updates from the ACLU and other groups.

“People see us as the last defense against totalitarianism,” said Howard Simon, the ACLU’s executive director in Florida, who said he was hiring more lawyers across each part of the state.

At the People Power launch, the activists streaming into the ­Watsco Center said they had been jumping on any cause they could handle, so long as it opposed Trump.

“I donated to the ACLU, then I donated to Planned Parenthood, and then I got the email about coming here,” Mayda Domenech, 46, said. “I couldn’t make it to the Women’s March, but I want to get involved.”

Rikki Goodman, 49, arrived at the launch event with a half dozen friends, all of whom had reactivated a dormant community group to focus on local needs and crises.

“The Democrats need to get back on the issues that count,” she said. “When they talk about whether [President Barack] Obama was wiretapping Trump — that’s a flare, that’s a distraction. You haven’t heard about [Attorney General] Jeff Sessions, and he’s doing things that we need to watch out for.”

The rally served up plenty for the activists to focus on. Dozens of volunteers in People Power T-shirts collected signatures for a ballot measure that would unwind Florida’s strict laws that make former felons go to great lengths to have their voting rights restored.

And the nine “freedom city” principles were ultra-specific, ready to be introduced at town hall meetings or called in to state legislators. One suggested that cities bar “surveillance of a person or group based solely or primarily upon a person or group’s actual or perceived religion, ethnicity, race, or immigration status.” Another would require immigration officials to have “a judicial warrant prior to detaining an individual,” while another would make it harder to arrest someone “solely on the basis of an immigration detainer.”

But the agenda went beyond the “freedom city” plan. Louise Melling, the deputy legal director of the ACLU, told activists that the Affordable Care Act was the “most significant civil liberties and civil rights legislation of this century.” There was no specific measure they could pass locally to defend it. Instead, she said, the ACLU would be on the side of defending Planned Parenthood funding — legal abortion being “a constitutional right” — and of giving advice for legal, effective protests.

“They’ve got some weeks where they want to get this through — we’ve got some weeks where we can tell them no,” Melling said. “We saw four senators change their responses as a result. We need you to call, tweet, write your members of Congress. Whether you speak matters.”

Said Romero: “We don’t have a PAC. We don’t register voters. Anybody who thinks the ACLU has become partisan needs to look at how hard we were on the Obama administration. We fought him tooth and nail on surveillance, on drones, on military commissions.”

Trump, however, was giving the ACLU challenges unlike any other president in Romero’s lifetime. When the People Power rally ended, most of its activists grabbed their signs and blue ACLU ribbons and headed to the half dozen food trucks lined up for an after-party. It was a way to keep the activists socializing; it was also a way to make a joke about the Trump supporter who warned of a Latino cultural takeover if immigration wasn’t halted.

“Taco trucks on every corner!” Shakir said as a DJ and break dancer entertained the crowd. “I was adamant about making this happen.”

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