A bipartisan deal to avert a government shutdown over the holidays collapsed Dec. 18 after President-elect Donald Trump issued new demands, including that Congress raise the debt ceiling to extend funding.

Trump’s push to torpedo the stopgap spending plan came as his billionaire ally Elon Musk, the co-chair of the Department of Government Efficiency, an incoming presidential advisory panel, spent much of Dec. 18 blasting the 1,547-page spending bill on X, his social network.

The bill, known as a continuing resolution, would have funded the federal government at current levels through March 14, while also providing more than $100 billion in disaster relief to help survivors of Hurricanes Helene and Milton. Government funding would otherwise lapse at 12:01 a.m. Dec. 21.

House Republicans were working Dec. 19 on a new plan that Trump endorsed, but it’s unclear if it will pass. Here’s what to know about a shutdown if lawmakers fail to agree by deadline.

How common are government shutdowns?

There have been 20 government funding gaps that ranged from one full day to 34 days since fiscal year 1977, according to the Congressional Research Service. There was an additional funding gap in 2018 that lasted only a few hours and didn’t result in government furloughs.

The most recent, a 34-day shutdown from late December 2018 to late January 2019 during Trump’s first term, was the longest in U.S. history. Under Trump, there was also a two-day shutdown in January 2018, plus the brief funding gap a month later.

During Democratic president Barack Obama’s second term, Congress’ failure to reach a budget deal in October 2013 produced a 16-day shutdown. Under President Bill Clinton, also a Democrat, there were shutdowns of five and 21 days in 1995 and 1996.

How are federal workers affected?

Before 1980, many federal agencies continued to operate during funding gaps, but then-Attorney General Benjamin Civiletti in 1980 and 1981 issued two opinions that required agency heads to suspend operations until funding was restored, except for operations regarding safety or otherwise authorized by law.

Around 800,000 federal workers were furloughed each day during recent shutdowns, affecting about 40% of the federal workforce, not counting active-duty military personnel and U.S. Postal Service workers.

Workers who remain on the job during shutdowns are not paid until new funding legislation is passed. Both furloughed and nonfurloughed workers historically received back pay, and a 2019 law guarantees that employees who work unpaid during shutdowns are guaranteed retroactive compensation.

There are about 2.28 million federal civilian employees.

What federal agencies are affected?

Because Congress hasn’t completed any of its fiscal year 2025 appropriations bills (the 2025 fiscal year began Oct. 1, 2024), all federal agencies and programs would be shut down once the current spending bill lapses, the White House Office of Management and Budget told PolitiFact.

The Office of Management and Budget is working with agencies as they review their contingency plans for a possible funding lapse, the office said.

The shutdown won’t affect mandatory spending, such as Social Security benefits, Medicare and interest on the debt.

Federal agencies would need to stop any activities funded by annual appropriations that aren’t “excepted” by law, the U.S. Office of Personnel Management said in 2021 guidance issued to agencies.

“Excepted” work includes emergency work, such as law enforcement, that protects the safety of lives and property. Employees whose work is not funded by annual appropriations, such as agencies funded by a continuing federal trust fund, are also excepted.

Each federal agency has contingency plans for shutdowns that determine which employees are “excepted” and which are furloughed. The plans would take effect if a shutdown happens, but could be updated.

A shutdown’s effects vary by agency. The Defense Department’s plan, for example, says active military members will remain on duty, but civilian employees will be furloughed. Some civilian employees, though, may keep working to carry out excepted activities.

The Veterans Affairs Department, meanwhile, said in its latest contingency plan published in January that about 414,000 of its nearly 460,000 workers are exempt because they are funded by multiyear funding or carryover money that won’t be expiring.

A Veterans Affairs spokesperson said that plan is in effect for now, and a shutdown would not affect veteran health care and benefits, or burials at its national cemeteries. Outreach, career counseling and regional offices would be affected, however.

Would a shutdown affect my holiday travel?

Transportation Security Administration agents and air traffic controllers are considered essential employees and will have to work through a shutdown, but without regular paychecks.

During the 2018-19 shutdown, holiday travelers faced delays as many unpaid TSA staff and air traffic controllers chose not to report for duty.

If you are planning to visit a national park, you may be out of luck. The National Park Service’s latest contingency plan says that, in general, its sites will be closed during a shutdown. People may be able to enter some parks through publicly accessible areas, but park rangers will be furloughed and restrooms and visitor centers would be closed.

Would I get my mail?

The U.S. Postal Service will continue to operate because it is funded by sales of postage and services and doesn’t rely on government spending bills.

What about Social Security?

Money for Social Security comes from a trust fund, not from government appropriations, so benefit checks will go out as usual.

Social Security Administration workers who cut the checks, however, are funded by Congress, and may face furloughs. Historically, the agency has been able to keep enough workers on the job to ensure that benefit checks are sent out uninterrupted.

The agency issued a contingency plan Sept. 25 that said about 50,000 of its roughly 59,000 workers would be retained during a shutdown and that “we will continue activities critical to our direct-service operations and those needed to ensure accurate and timely payment of benefits.”

What happens to federal courts?

In previous shutdowns, federal courts have shifted money around to keep key operations running, though civil cases and building maintenance were affected. Pay for judges can’t be cut, but some court staff may not be paid until the shutdown ends.

How else could this affect me?

Here are some of the federal activities that stopped during one or more past shutdowns, according to the Congressional Research Service and the Committee for a Responsible Federal Budget:

• The Centers for Disease Control and Prevention ceased disease surveillance, and hotline calls about diseases went unanswered at the National Institutes of Health.
• Recruitment and testing of federal law enforcement officials, including Border Patrol agents, stopped.
• Visa and passport services stopped.
• Safety inspections for food, workplaces and hazardous waste sites stopped.
• Mortgage approvals were delayed because the Internal Revenue Service couldn’t verify income and Social Security numbers.

PolitiFact senior correspondent Louis Jacobson contributed to this report.

This fact check was originally published by PolitiFact, which is part of the Poynter Institute. See the sources for this fact check here.