What happens in a government shutdown?

The federal government shut down at midnight after the Senate failed to muster the 60 votes needed to keep it funded. It’s the first time this has happened when one party controls the White House and Congress.

But this shutdown, which happened on the one-year anniversary of Donald Trump’s presidency, doesn’t mean every U.S. department or agency will close. Here’s the lowdown on what you need to know.

Which agencies are closed?

Whether agencies and departments close or remain open depends on their level of importance. Workers at agencies and departments that are considered nonessential would stop working until a bill is passed, according to CNN.

Employees in “nonessential” departments will be placed on furlough — a temporary leave for employees due to special conditions, like not having money to fund operations. In the 2013 shutdown, about 850,000 employees were furloughed per day, according to the Office of Management and Budget.

Roughly half of the Department of Health and Human Services’ 80,000-member staff would likely be furloughed, Vox reported. That includes people who monitor outbreaks, such as this season’s flu epidemic, at the Centers for Disease Control and Prevention.

What departments are essential? Who decides?

The typical course of action is that employees who perform “emergency work involving the safety of human life or the protection of property” remain on their jobs during a shutdown. Senior executives and legal advisors at each agency have traditionally decided who works and who doesn’t, per Politifact.

For example, the military is considered essential and would still report for duty, CNN reported, but troops may not get paid. Federal courts would also remain open, according to the Huffington Post.

Do federal employees, working or not working, still get paid?

Yes and no. Employees still get paid. But don’t expect the checks to come as quickly as they normally do. Marc Goldwein, senior policy director of the Committee for a Responsible Federal Budget, told FOX News that “an employee loses their paycheck at the time he or she needs it.”

Federal workers typically receive back pay after they return to work, FOX reported. In previous shutdowns, everyone was paid retroactively, CNN reported.

Trump will continue to be compensated, according to The Washington Post, which cites a Congressional Research report that says the Constitution forbids the president’s salary to be reduced while he or she is in office.

The report says Congress members would continue to work due to their “constitutional responsibilities” and “a permanent appropriation for congressional pay.” Whether or not their staffers would keep working would be left up to the individual lawmaker.

What about museums and parks?

The Smithsonian Institution tells NPR its museums in Washington, D.C., along with the National Zoo, would remain open this weekend, but will close on Monday if the government is still shut down.

You may still be able to visit the nation’s parks—but that access would likely be limited.

A spokesman for the National Parks Service told The Sacramento Bee that in the event of a shutdown, national parks will “remain as accessible as possible.” The shutdown would only affect parts of the park that require staffing, such as restrooms and concessions that have some federal employees, the newspaper reported.

How long does a shutdown last?

It depends on when an agreement is reached in Congress. The 2013 shutdown lasted 16 days.

So what does this mean for the country?

It could cost the country billions in lost economic activity. In 2013, the payroll cost of furloughed employees’ salaries was about $2 billion, according to the Office of Budget and Management.

Social Security checks will continue to be mailed, as the process is largely automated, NPR reported. But Social Security cards won’t be issued. Medicare is considered a critical agency and would remain open, The Sacramento Bee reported.

The U.S. Postal Service, which is independently funded, would keep operating, meaning mail will still be delivered, according to the Huffington Post. The Transportation Security Administraton would still be funded, so air travel is expected to continue.

This story was originally published January 18, 2018 at 1:15 PM with the headline "What happens in a government shutdown?."