Smithsonian curator Lisa Kathleen Graddy searches for pins, buttons and accessories at the Democratic National Convention. (Dan Zak / The Washington Post)

PHILADELPHIA — The curator pauses at the edge of the convention floor, which is a living archaeological site. Artifacts are everywhere, and they are attached to people.

Buttons, pins, hats, signs: all representing the Democratic National Convention, which will soon be over and lost to the ages.

It's 4:11 p.m. Thursday and the curator has 60 minutes left on her temporary floor pass to excavate physical evidence that could prove one day to future generations that this convention happened. She steps onto the floor and begins craning, squinting, scurrying — looking for attendees who might surrender their stuff to posterity.

"People are amazingly kind," says Lisa Kathleen Graddy, of the Smithsonian's National Museum of American History, as she carries a tote bag past the Colorado delegation. "They're intrigued and flattered that one of their possessions will be part of the national story."

That story is unfolding and forever in dispute, so tangible objects at pivotal moments like this have a certain importance. Heartsick supporters of Bernie Sanders, for example, are relieved that the Smithsonian is acquiring and preserving the symbols of the Vermont senator's vanquished campaign.

"We're gonna go up here," Graddy says, climbing the steps of section 115, "because I'm interested in things that show delegation unity."

Graddy takes a photo of the New Mexico delegation’s attire and accessories. (Dan Zak / The Washington Post)

Graddy, who lives in Alexandria, Va., collects a bandanna from New Mexico that features a symbol of the Zia people, then walks back down the steps and clockwise around the floor, head swiveling and phone poised to take photos.

"I'm just curious about your sign," she says to a South Carolina delegate.

"Can you tell me about your button?" she says to a Virginia delegate sporting a "TRUMPBUSTERS" symbol. The delegate tells her that he bought it for $10 from a bearded Wyoming delegate who drove to Philadelphia in a Tesla.

A Virginia delegate’s button catches Graddy’s eye. (Dan Zak / The Washington Post)

"I gotta get to Wyoming," Graddy says, mindful of the time. The arena floor is a swirling stew of bodies. It is impossible — and also against the rules — to stand still. Everyone is in a rush, angling for a photo, giving an interview, watching the stage, watching their phones. Their Snapchats zip into the air and disappear, gone forever. Graddy thinks political signage is part of a visual conversation that continues through a campaign, and through the decades. Her fellow curator Jon Grinspan, who was also with her at the RNC in Cleveland, boils their mission down to a question: "If you want to learn about 2016 in 100 years, what should you find?"

What they find at these conventions will join 100,000 other objects in the political-campaign collection of the National Museum of American History.

[This is what it feels like at the Democratic National Convention]

"Someone did this work for us in the past," Grinspan says. "Someone in 1896 did this work for us."

Graddy asks a volunteer for directions to the Wyoming seats, which at Wells Fargo Arena is near Ohio, but Graddy remembers something from yesterday's excavation: "You know what? I gotta get to California. Someone promised me a T-shirt." It says "carpenters support Hillary," and she thinks it belongs in the Smithsonian's archives because it's both specific and general.

A volunteer points curator Graddy to the Wyoming delegation at the Wells Fargo Center. (Dan Zak / The Washington Post)

But she can't find the man from California, so she heads into the concourse and over to section 109, up a set of stairs, and shuffles past people's knees to the Wyoming delegation, where she sees a "TRUMPBUSTERS" button on delegate Samantha Rise Roberson. Graddy introduces herself, extends a business card, tells her she'd love to find the man with the buttons. Roberson doesn't know where he is, but she unpins her own and gives it to Graddy. As our physical world shrinks in the digital age, Roberson says, these talismans are precious.

"Our delegation is small and, though it's been difficult, we had a four-hour conversation and decided our ultimate goal is to stop Donald Trump," Roberson says of the state that Bernie Sanders won. "That button represents what we're doing. So I'm happy to send it off."

Wyoming delegate Samantha Rise Roberson gives her “TRUMPBUSTERS” button to Graddy. (Dan Zak / The Washington Post)

Graddy drops the button in her tote. As she doubles back, she sees a fabulous hat between the Idaho and Virgin Islands delegations. It is a wizard hat wrapped in shiny silver paper. "Oh that is so wonderful," she says. "But it would fall apart." She pauses, thinks, sighs. "All right, I need that hat."

She heads for the concourse and re-emerges into the arena near the Virgin Islands. The man under the hat is delegate Edgar Phillips. Everyone wants a selfie with him. But Graddy wants his hat.

"This hat is amazing!" she says to Phillips. "I know you may not want to part with it …"

Graddy chats with Edgar Phillips, delegate from the Virgin Islands. (Dan Zak / The Washington Post)

"When I get back to the islands," Phillips says, taking a business card, "I'll ship it to you."

Why does Graddy want this ridiculous hat? Why should it be shipped over the ocean back to Washington and stored at the Smithsonian Institution?

"It's amazingly unique," she says. "It's just oddly complicated. And it has all different pictures of Hillary. The shape is interesting. I haven't seen many objects that are individually constructed. And it's from the Virgin Islands."

One day, someone will search the Smithsonian archives and find the hat, and see the symbolic impact of Hillary Clinton and the creativity of one delegate from the Caribbean. And now it's 5:12 p.m. and Graddy's time in the present is up. She heads off into the future, with the past in her tote bag.