Some of the volunteers were children or grandchildren of refugees. Their synagogue, Am Shalom (“People of Peace”) in Glencoe, Ill., displays a statue depicting members’ families who perished at the Nazis’ hands. The Syrian family, and the president’s orders, were coming on International Holocaust Remembrance Day, some of the volunteers noted with tears in their eyes. A hundred synagogue members had contributed in some way to helping resettle the Syrians: renting an apartment steps from a playground, assembling a vacuum cleaner, lining up juice boxes in the refrigerator.
Some of the synagogue members had signed on instinctually, so the Syrians would be helped the way their own parents or grandparents had been aided when they arrived in the United States. Others had joined as a way of countering Mr. Trump — just a few of the many Americans, of varied backgrounds, reacting with shock, outrage and concern to his curtailment of the country’s long-established refugee resettlement system.
“The Statue of Liberty has always been our symbol of welcome,” Rabbi Steven Stark Lowenstein, the group’s leader, said at the airport. “It feels like Trump turned off the light,” he said.
At the Pentagon on Friday, the preparations for the president’s actions were orderly: High-level officials gathered in a room called the Hall of Heroes, and photographers assembled. But around the country, refugees, resettlement workers and volunteers expressed panic. Resettlement workers did not know if they would have jobs once Mr. Trump’s refugee and immigration plans have been fully carried out. Volunteers wondered what they would do with furniture and money they had collected for refugees who were supposed to arrive soon.
RefugeeOne, the resettlement agency responsible for the family coming into O’Hare, had been expecting another Syrian family to arrive on Monday.
“That’s not happening,” Kim Snoddy, the program’s liaison to groups like the Am Shalom volunteers, said as she waited with them at the airport on Friday.
A volunteer from another Chicago group posted a photograph on Facebook of an empty crib, made up with a pink sheet and a stuffed bunny, for the baby of a family that would no longer arrive.
Resettlement workers and volunteers across the country said that since Election Day, Americans of diverse backgrounds had been lining up to aid refugees, channeling their opposition to Mr. Trump into a desire to help vulnerable newcomers. Sloane Davidson, 37, a graduate student in Pittsburgh, hosted refugees for Thanksgiving dinner and said she was so moved by the experience that she took a job as a case aide at a local agency.
“The more I learned about what I felt to be the truth and the truth that Trump was telling,” the more she wanted to get involved, she wrote in an email.
Resettlement agencies said that volunteers had been swarming their offices and that even more had surfaced last week when Mr. Trump’s specific plans became public. When the International Refugee Assistance Project put out a call for lawyers to help new arrivals in danger of being turned away, it received 3,000 volunteers in four hours, said Becca Heller, the organization’s director.
“People are desperate to help refugees as a way to counter these discriminatory policies,” she said.
As the minutes passed at O’Hare, the volunteers checked the time again, tense with the knowledge that Mr. Trump was about to commit pen to paper. The family they were awaiting had flown into Washington the night before, meaning they had cleared immigration with less than a day to spare. But the volunteers said they would not be able to exhale until the newcomers landed in Chicago. The flight was delayed, they heard. They glanced at the time on their phones again.
As soon as the Syrian family of four stepped into the baggage claim area, the synagogue members surrounded them protectively, offering the flowers and signs, as a resettlement worker translated. Because they spoke no English, the newcomers wore tags around their necks, like Paddington Bear, so if they got lost, they could be identified.
In a moment, the two Syrian children’s arms were laden with gift bags of toys. The parents said they were too terrified to talk to a reporter, out of concern for family members — some still trapped in dangerous areas of Syria and others who had been cleared to travel to the United States but had not yet received plane tickets.
After hugs and snapshots and many professions of welcome and thanks, the group at the airport dispersed. The refugees headed to their new home with a few escorts, the synagogue members back to their far more stable lives. Just before they parted, Rabbi Lowenstein gathered his congregants and gave them a charge.
“If this is the last group of refugees to get in, we will show them the best of America,” he said.
The family was driven to its new home, where a meal and a Syrian-style semolina cake were waiting. The couple said they had not checked the news since landing in the United States, and no one from the volunteer group had told them what was about to happen. Moments before they arrived at the cozy, fully stocked apartment, Mr. Trump, wearing an American flag pin, signed the orders in front of an audience of his advisers and Pentagon officials. As he finished, the clapping in the room was loud.
Behind him hung an oversize medal depicting the Statue of Liberty, a beacon of welcome.