With her Smithsonian ID card dangling from her neck, Dwandalyn Reece summoned the museum staff to almost exactly the spot where President Trump had stood days earlier, posing for a picture with a Bible.

The half-dozen men and women approached in jeans and masks, clutching cameras, notebooks and pencils in glove-covered hands as they stared up at St. John’s Episcopal Church, where every president since James Madison has attended services. They looked sweaty, a little nervous and nothing like a team of superheroes, although that’s how some passersby hailed them.

“Thank you guys so much,” said a woman walking by, who’d spotted Reece’s Smithsonian card, “for being here.”

Reece nodded at her, then cocked her head and considered what words could possibly capture the significance of what they were about to do. Smithsonian staff were at Lafayette Square to collect mementos from the historic protests over George Floyd’s death, which had roiled the nation’s capital — and the country. After days of deliberation, museum employees had decided they must preserve what they could, as a first step toward creating a future exhibit or collection capturing the moment. The exhibit may not appear for months, maybe years, if at all.

Now, Reece thought back over the past 12 days, when thousands had filled Lafayette Square every afternoon, hoisting handmade signs and shouting “Say his name!” They had rattled a tall metal fence erected outside the White House to protect the president — and later converted the wall into a crowdsourced memorial, filled with hundreds of pictures and posters meant to honor black lives lost at the hands of police.

That fence would come down the next day. Late the night before, demonstrators had prepared by moving signs and faded flowers across the street, re-sticking the artwork to a wooden construction wall in hopes of preserving it. That same desire had driven Reece here on a hot day, as she reminded her colleagues: They had to collect history before it disappeared.

“We need to have sensitivity so we can make our best decisions about what we take and what we don’t,” said Reece, associate director of curatorial affairs and curator of music for the National Museum of African American History and Culture. “This is a really important moment.”

Smithsonian museum staff had been weighing when and how to collect material from the protests for more than two weeks. But on a call earlier that morning last week — worried by reports from the National Park Service that it planned to dismantle the White House fence Wednesday afternoon — Aaron Bryant, a historian studying social protests who leads the African American Museum’s rapid response collecting team, made a decision.

It was time.

“Moments that are generally kept and captured by history are moments where . . . something has happened to change the way people look at things, talk about things and engage with each other,” Bryant said in an interview. “You could see it on television, how many people were out in the streets. You could tell that the nation was in the midst of a transformation.”

On Wednesday, almost as soon as Reece finished speaking, staffers from three Smithsonian institutions — the African American Museum, the National Museum of American History and the Anacostia Community Museum — split and spread across the sunlit square, renamed Black Lives Matter Plaza a few days before by the District’s mayor. The three museums have formed a coalition, and would work together to gather material.

The staffers traveled in small groups, weaving through strolling families and past newscasters still broadcasting live from Lafayette, although the number of protesters was dwindling every day. They headed not for the wall of objects, but for the people guarding it.

Mary Elliott, curator of American slavery at the African American Museum, approached a man wearing a “Black Lives Matter” face mask. She leaned against a lamppost and told him she liked his mask, which led to a discussion of where he’d bought it, which led to the revelation that he’d lost his job after skipping work to protest.

Elliott stood suddenly straight.

“I’m from the Smithsonian,” she said, “what’s your name?”

Sean Bruegman, 26, told her. He explained that he is a resident of Anne Arundel County in Maryland and Indian American, although he “looks white.” He’d been working as an executive chef in a restaurant before the pandemic, he said, but the virus shut it down. Although it reopened just as the Floyd protests began, Bruegman decided to demonstrate instead of showing up for work.

“The next day they said they needed a new executive chef,” Bruegman said, shrugging. “But it was worth it.”

Elliott asked him if he would follow her back to St. John’s, where some colleagues stood with recording equipment and note pads upon which they could take down his contact information. She said the museum wanted to tell his story. Bruegman hung back, hesitating, and pointed at his white skin. He asked if she was sure she wanted to talk to him.

“Oh yes,” Elliott said. “That’s an important story.”

This is how museum collecting works, Bryant said later. People might suppose staffers would head straight to pull posters from walls, or to snatch objects left in the street, but best practices dictate speaking to people on the ground first. It is key to build connections with demonstrators — both as a way of earning their trust, and because the most memorable museum exhibits center on human lives.

“It’s through the specificity of a particular experience that we can all relate, somehow,” Bryant said. “So, the gentleman who lost his job — my job is to make sure his story moves from the margins to the center.”

Still, in coming days and weeks and months — perhaps years, Bryant said, because collecting can continue for decades — the museum will seek physical keepsakes, too. Staffers will hunt down buttons, banners, hats and T-shirts, from the streets of D.C. and from other cities where the Floyd protests have upended daily life and forced an unprecedented reckoning with the role of police.

Whether and when the collected objects will appear in an exhibit is unclear, Bryant said. As he strolled along the wall of artwork Wednesday, certain sights sparked various visions: An especially colorful poster led him to ponder a social justice-themed art collection, filled with banners, signs and music. When he glanced at demonstrators chatting and hanging artwork nearby, many of them decked out in “Black Lives Matter” shirts and masks, he envisioned a fashion exhibit.

“The possibilities,” he said, “are endless.”

The sun rose higher, sweat droplets splattered notebooks and museum staff settled into the space they hoped to capture, reconfigured on cool museum walls, for generations of Americans to come.

Elliott paused to regard a poster that referenced both Colin Kaepernick and former secretary of defense Jim Mattis. Bryant touched a forefinger to a spray-painted “#ABOLISHICE” slogan. He pulled out his iPhone and snapped two pictures of a sign that asked Americans to respect black culture, as well as a sign that quoted Malcolm X.

He came to a full stop in front of a sandal-clad white woman, who was standing with a small group and gripping a poster that announced, “The reason you don’t see cops shutting down KKK rallies is the same reason you don’t see Hannah Montana & Miley Cyrus in the same room.”

Kasandra White, it turned out, was happy to chat. She told Bryant that she and her companions — her friends Taeya Teasley, 23, and mother-and-son pair Brandy Gardner Berg, 43, and Jaxon Berg, 19 — had driven from Salisbury, N.C., for the day. They were heading back that afternoon. They had not wanted, White said, to miss out on witnessing history.

Bryant waited until she finished explaining her poster’s slogan (“It’s because Hannah Montana and Miley Cyrus are the same person, see”) before introducing himself, mentioning what he does for a living and making the ask: Might she, please, be willing to hand over the poster?

White smiled and folded the white sheet carefully into quarters. Bryant held out two hands to accept it. As the paper slid between his palms, he felt a thrill of gratitude.

Then he felt the weight of responsibility.