WASHINGTON — A North Carolina National Guard infantry battalion called off a training exercise that had been planned for a year. Flu samples from around the country will no longer be collected and tested. A skeleton staff of workers at the Internal Revenue Service girded themselves to answer a deluge of questions about the new tax law.
The vast machinery of the federal government began grinding to a halt on Saturday morning, hours after the Senate failed to reach a funding deal. But like an aircraft carrier after its propellers stop turning, much of the bureaucracy will stay in motion for a while, and some essential services, like the armed forces, the post office and entitlement programs, will not stop working at all.
Tens of thousands of federal workers woke up to notices from their cabinet secretaries informing them that, barring action from Congress, they will be furloughed this coming week. The shutdown is falling unevenly: The Education Department will send home more than 90 percent of its 3,934 employees, while the Pentagon said the entire uniformed military, and half of its civilian work force, would continue to serve. But for now, even the troops will not be paid.
At the White House, three-fifths of President Trump’s staff will be placed on temporary leave. The National Security Council will stay at full strength, but about 60 percent of the president’s closest aides were to be furloughed. Others could come to the White House or telecommute, but only for up to four hours, and only to execute an orderly shutdown.
Experts on the government said the sense of confusion and dislocation was being amplified by the Trump administration’s slowness to advise staff agencies, the unusually high rate of turnover in federal ranks, and the lack of planning for a shutdown that few in the White House expected to happen.
“As bad as it would be any time, it will be worse this time,” said Max Stier, president of the Partnership for Public Service, a nonprofit group that studies the federal government. “Most agencies did a very poor job of communicating with their work forces. They didn’t prime the pump.”
Yet millions of Americans will not notice the effect of the shutdown on their daily lives, and some of the most visible examples of previous government shutdowns — the closing of national parks — will not happen this time. The Interior Department said attractions like the Grand Canyon and the World War II Memorial on the National Mall would be open to visitors, though the National Park Service will close its offices and no longer provide services like cleaning restrooms, collecting trash and plowing roads.
The last time Congress failed to agree on a budget, in 2013 during the Obama administration, a group of veterans, aided by Republican lawmakers, knocked over barricades to visit the World War II Memorial. This time, said Heather Swift, a spokeswoman for the Interior Department, “the American public and especially our veterans who come to our nation’s capital will find war memorials and open-air parks open to the public.”
Critics said the decision to keep the parks open smacked of politics. “Gates would be open and people could enter, but there would be virtually no staff on hand to protect them or the parks’ resources,” said Theresa Pierno, the president and chief executive of the National Parks Conservation Association. “It’s an irresponsible way to run parks.”
The Smithsonian Institution and its National Zoo will also stay open at least through Monday. All told, the Park Service will furlough 21,383 of its 24,681 employees, while the Interior Department will send home more than three-quarters of its 70,000 workers.
Another federal institution that will stay open, at least temporarily, is the Environmental Protection Agency. The agency’s administrator, Scott Pruitt, told the staff on Friday that it had a financial cushion that would allow it to operate through next week even if government funding expired. “All E.P.A. employees should follow their normal work schedule for the week of Jan. 22, 2018,” Mr. Pruitt wrote in a memo. Most of the agency’s nearly 14,500 employees will be furloughed after that money runs out.
Some cabinet members put a spotlight on the damage they said a shutdown would inflict on the public. The education secretary, Betsy DeVos, said, “A protracted delay would severely curtail the cash flow to school districts, colleges and universities and vocational rehabilitation agencies that depend on the department’s funds to support their services.”
Many school districts, Ms. DeVos wrote, receive 20 percent of their operating funds from the department, while colleges rely on federal funds to pay workers who help retain disadvantaged students. Moreover, the government pays about 80 percent of the cost of providing services to individuals with disabilities who are in vocational programs.
The Pentagon tried to project an image of business as usual, though the shutdown will curtail training, maintenance and medical facilities. The effects were particularly jarring at Fort Bragg, in North Carolina, where hundreds of National Guard soldiers, engineers and civilian contractors had mobilized for a mock armored assault — an exercise nearly a year in the planning.
At midnight, with the Senate still in an impasse, the exercise was called off, the soldiers turned in their weapons, and the tanks returned to their motor pools. By late Saturday morning, everyone headed home.
Defense Secretary Jim Mattis vowed in a memo to his staff on Friday that he would try to mitigate the effects of the shutdown, both personal and financial. Among those are the loss of $100,000 gratuity benefits to families who lose a service member, as well as government-funded travel to funerals and transfers of the dead at Dover Air Force Base, according to the nonprofit Tragedy Assistance Program for Survivors. The wars, however, will go on.
“We will continue to execute daily operations around the world — ships and submarines will remain at sea, our aircraft will continue to fly and our warfighters will continue to pursue terrorists through the Middle East, Africa, and South Asia,” Mr. Mattis wrote.
At home, the Postal Service, which has funded its operations since the 1970s by selling stamps and other services, will remain open. The government will continue to cover more than 100 million elderly, disabled or low-income people through Medicare and Medicaid. Entitlement programs are not directly affected by the lapse in appropriations.
The Trump administration said that federal officials would continue making payments to states for the Children’s Health Insurance Program, using funds that remain unspent from prior months. But funds are running out in many states, and some have notified parents that their children could soon lose coverage if Congress does not act.
Likewise, although the Social Security Administration will furlough more than 10,000 employees, more than 52,000 will stay on to continue paying benefits and performing other essential duties. About 62 million Americans, including retirees and disabled workers, receive Social Security benefits.
“Everybody is concerned about their Social Security check,” Representative Carolyn B. Maloney, a Democrat from the Upper East Side of Manhattan, said before she went back into negotiations at the Capitol. “And 90 percent of Homeland Security will continue, which is important to people in New York.”
Ms. Maloney noted that the investigation by the special counsel, Robert S. Mueller III, into ties between the Trump campaign and the Russians would also not be interrupted by the shutdown. Nor will proceedings at federal courts, at least for a few weeks. The courts will remain open and can continue operations through Feb. 9, using court fees and other funds.
Most proceedings will occur as scheduled, according to the Administrative Office of the United States Courts. In cases where a federal lawyer is not working because of the shutdown, hearings may be rescheduled.
Federal officials also promised that there would be no disruption of the school lunch program or food stamps, now known as the Supplemental Nutrition Assistance Program. The Food Safety and Inspection Service will continue inspecting meat, poultry and egg products.
While roughly half of the work force at the Department of Health and Human Services will be furloughed, the department said it would continue services that involve the safety of human life or the protection of property. Those include a suicide prevention hotline, patient care at the National Institutes of Health, and product recalls and other consumer protection services run by the Food and Drug Administration.
At the I.R.S., however, the shutdown will burden an already understaffed agency that is staggering under a crush of questions related to the new tax law. The Treasury Department said 45,479 people, or 56 percent, of the I.R.S.’s staff would be furloughed. Because of budget cuts, the agency has lost some 21,000 employees since 2010.
Tony Reardon, president of the National Treasury Employees Union, warned this past week that a shutdown would stress an already strained tax system, and that it would be the fault of Congress and the Trump administration, not federal workers, if problems arose.
Mr. Stier of the Partnership for Public Service said, “I don’t think anyone has thought of the implementation of the tax bill in the context of a shutdown. People totally underestimate how difficult this is.”