The threat of a government shutdown looms over Washington this week, as President Donald Trump was set to meet with key congressional leaders at the White House on Monday, Sept. 29, less than 48 hours before a shutdown could be triggered.

With Democrats pushing a series of health care demands, and Republicans refusing to budge, a deal had not been reached by Monday afternoon, Sept. 29. Barring a breakthrough, "essential" government services such as the military and law enforcement will keep working, but "non-essential" functions like national parks will close or cut staffing starting Wednesday, Oct. 1 at 12:01 a.m.

"If it has to shut down, it has to shut down," Trump told reporters Sept. 26.

Republicans hold a majority in the House of Representatives and a 53-47 edge in the Senate, which requires 60 votes to pass a funding bill, meaning that seven Democrats − in addition to all 53 Republicans − would need to support the legislation.

Here's what you need to know about a government shutdown.

What is a government shutdown?

Each fiscal year, Congress appropriates funds for federal agencies to operate. If Congress does not agree on appropriations or a temporary spending bill (called a continuing resolution), the affected federal agencies must effectively shut down or stop normal spending, according to the United States Office of Personnel Management (OPM). An exception is made for certain jobs or services deemed essential, which continue to operate.

When could a government shutdown happen?

The current funding for the government expires at midnight on Sept. 30, with 12:01 a.m. on Oct. 1 being the potential start of a partial government shutdown.

How many government shutdowns have occurred in the past?

Over the last five decades, there have been 21 federal shutdowns, many of which lasted only a day or two. One of the most recent shutdowns was also the longest, lasting 34 days between December 2018 and January 2019, during Trump’s first term in office, due to a stalemate between the president and Congress over border security.

What happens during a government shutdown?

During a government shutdown, all federal agencies and services that officials do not deem "essential" must stop working.

Essential services include the U.S. Postal Service, Medicare and Social Security services and air-traffic control.

"Non-essential" work, however, comes to a halt, affecting thousands of federal employees and millions of Americans. National parks closed during past shutdowns or were kept open with state help – but with fewer services like trash pickup.

Does the military shut down during a government shutdown?

All active-duty U.S. military personnel stay on the job, but nearly half of the Department of War's 741,477 civilian employees could face furloughs, according to a contingency plan released by the department. Another part of the military that would remain on the job would be the National Nuclear Security Administration, which oversees nuclear weapons.

What happens to law enforcement during a government shutdown?

Federal law enforcement agencies, including the FBI, DEA and prison staff will remain operational. The Secret Service and Coast Guard will continue their duties.

What happens to national parks?

National parks, monuments and other sites will close to the public, with rangers furloughed and facilities shut down. Some states may temporarily fund park operations, as seen during the 2018-2019 shutdown.

What happens to Social Security and Medicare?

Both retirement and disability benefits proceed without interruptions. Medicare and Medicare benefits also continue, but some delays could be seen.

What happens to veterans’ benefits and food assistance during a shutdown?

Similar to Social Security, veterans continue to receive their benefits and medical care. Programs like the Supplemental Nutrition Assistance Program (SNAP) will also continue, though there could be minor disruptions.

Does a government shutdown impact borders and Homeland Security?

Border Patrol and immigration enforcement agents will continue working. However, local governments will not receive new aid for migrant shelters.

Transportation during a government shutdown

Airport security screeners and air traffic controllers will remain on duty, but new hires and some major infrastructure projects could face delays. Absenteeism, as seen in previous shutdowns, might impact airport operations. Each federal agency develops its own shutdown plan based on prior shutdowns and guidance from the Office of Management and Budget (OMB), according to the Committee for a Responsible Federal Budget.

About 800,000 federal employees went without pay for 35 days during the longest-ever U.S. government shutdown in 2018 and 2019, as USA TODAY previously reported.

Contributing: Reuters; Terry Moseley, Eric Lagatta, Fernando Cervantes Jr., Bart Jansen, Zac Anderson, USA TODAY

Saman Shafiq is a trending news reporter for USA TODAY. Reach her at sshafiq@gannett.com and follow her on X and Instagram @saman_shafiq7.

This article originally appeared on USA TODAY: What is a government shutdown? Here's what it means and how it works

Reporting by Saman Shafiq, USA TODAY / USA TODAY

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