Crowds gather at the Smithsonian National Zoo amid a partial shutdown threatening to shutter the zoo until the government reopens. (Jahi Chikwendiu/The Washington Post)

By all accounts, Saturday was a near-perfect day to be a tourist in Washington. It was unseasonably warm, and the sun cast a soft orange glow on the monuments and cupola, creating the postcard-like scene that draws so many visitors to the city. Legions of strollers took to the winding paths of the National Zoo, where a tiger’s deep bellow rang out over the chatter of visitors.

But the partial government shutdown cast a shadow on the day.

So far, the Smithsonian Institution’s museums, research center and zoo have been spared from the shutdown that has furloughed thousands of federal employees. But if the closure continues beyond New Year’s Day, all Smithsonian institutions will shutter, locking visitors out of tourism mainstays like the National Zoo, the National Museum of American History and the National Museum of African American History and Culture. The National Gallery of Art Sculpture Garden ice rink, where visitors can skate in the shadow of the National Archives building, will also close.

“We have no control over this,” said Linda St. Thomas, spokeswoman for the Smithsonian Institution.

She lamented that closures were bound to disappoint visitors next week, many of whom make visiting the free museums a central part of their trips to the nation’s capital. Tourists often have their heart set on seeing the 45-carat Hope Diamond at the National Museum of Natural History, or the portraits of the Obamas at the National Portrait Gallery.

“The Smithsonian museums are a big part of a person’s trip to Washington,” St. Thomas said. Luckily, it is slow season, she said, so a closure will affect far fewer travelers.

The partial shutdown is set to be one of the longest in history, the result of an impasse between President Trump, who is demanding billions for a border wall, and congressional Democrats, who refuse to authorize the funding. There were few signs the shutdown would end anytime soon, with Trump tweeting threats to shut down the entire southern border if he did not get funding for the wall. Lawmakers are not scheduled to return until at least Jan. 2.

The shutdown has meant about 800,000 federal workers are without paychecks during the holiday season, plunging many low-wage workers into economic peril.

The Smithsonian is set to be the latest tourism casualty of the shutdown, which has also suspended the work of the National Park Service. That meant hikers at Great Falls Park in Virginia were locked out of park restrooms and that rescue and emergency services were limited. At Joshua Tree National Park in California, the holiday season is the busiest time of the year with families on break camping and rock climbing.

But this year, the rangers have been sent home and volunteers have been buying and restocking toilet paper and even scrubbing toilets. One camper put up an American flag upside down, as a sign of distress.

Bruce Damon, owner of Nomad Ventures, a backpacking supply shop that works in the park and said that since the government shutdown, “we have had some people volunteer to keep the park clean because of the bathroom situation.”

“It feels like we are just pawns,” said Damon. “The parks are so underfunded as it is, it just feels like such a slap in the face.”

He said they sold at cost “wag bags,” which allows volunteers and campers to clean up waste.

There’s also been a host of illegal camping practices and visitors putting Christmas lights around endangered Joshua trees they are supposed to leave untouched, said Joe De Luca, who started a group called Climbers’ Collective.

He said he felt strongly that the park should be closed down.

“Closing Joshua Tree during the busiest part of year would upset people . . . so it’s open without staff, and 90 percent do fine, but 10 percent do some damage to a delicate environment,” said De Luca.

The Smithsonian Institution employs about 4,000 federal employees, many of whom will be furloughed after Jan. 1, joining the 350,000 others who have been off the job since the start of the shutdown. As in other federal departments, essential staff will remain on the job.

At the National Zoo, that means caretakers — including veterinarians and nutritionists — will remain on hand for the lions, tigers, bears and other creatures. Museum security staff will also stay on the job, as will the approximately 2,000 Smithsonian staff whose work is not funded by the federal government.

Lucy Asmat, a 53-year-old nurse visiting from Lima, Peru, watched prairie dogs peek out of dirt holes in their mound-like habitat Saturday. She said a closure would be deeply disappointing for tourists who had traveled great distances to see Washington.

“I understand there are priorities,” Asmat said. The attractions “are not just for Americans. They are for foreigners, like us, who want to see all the beautiful things that you have in the United States. The wall should not be a priority.”

Heather Randell, 35, came to the zoo Saturday with her husband and 7-month-old son Jules. Randell, an environmental sociologist at the University of Maryland, said a potential zoo closure worried her, but not as much as other consequences of the shutdown, like federal employees going without paychecks.

“I care more about inaction over environmental issues,” Randell said.

Some tourists enjoying the very attractions that could shut their doors Wednesday said they back the president’s stance on the wall, even if it means they will have to change their itinerary.

Ralph Pariente Jr., who traveled from Miami, explored the National Gallery of Art Sculpture Garden with his wife and 10-year-old son, his neck wrapped in an American flag scarf. He said he backs Trump and believes the border wall is necessary to stop or slow illegal immigration.

“I agree with the shutdown,” Pariente said. “I feel bad for the employees who aren’t getting paid. . . . But nothing ever gets done.”