The US is potentially facing another federal government shutdown. President Donald Trump wants $5.7 billion to fund a border wall with Mexico. The Democrats who took control of the House of Representatives in November’s midterm elections are refusing to give it to him. But how does political disagreement over a single issue bring the federal government grinding to a halt?

Why do shutdowns happen?

It all traces back to the Constitution, the founding law of the United States which came into force in 1789.

It separated the US government into three branches: the legislative (Congress, divided into the Senate and the House of Representatives); executive (the President); and judicial (the Supreme Court and other federal courts).

Crucially, the Constitution gave Congress the sole authority to decide what money could be spent on, stating: “No Money shall be drawn from the Treasury, but in Consequence of Appropriations made by Law” (Constitution of the United States, Article 1, section 9, clause 7)

Image: US National Archives

Both chambers of Congress – the Senate and the House of Representatives – need to pass 12 appropriations bills to allocate funds to different government agencies and departments, usually by 1 October each year. If either refuses to pass a bill, a short-term extension can be agreed. Otherwise, the money stops flowing.

The President can veto a bill, but cannot change it. So if he disagrees with Congress over one particular issue, his options are either to pass or block the bill as a whole.

What keeps running?

Every shutdown is slightly different depending on which appropriations bills are caught up in the legislative standoff.

Under the Antideficiency Act no US government agency or department can spend or enter into a contract unless the full funds have been appropriated – they have to “pay as you go”. The only exceptions are operations that are essential for the safety of human life or protection of property.

So federal law enforcement officers, military personnel on active duty, air traffic controllers, airport security staff, and doctors and nurses in federal hospitals are all required to keep working.

The postal service is independently funded, so the mail is delivered.

Government benefits like Social Security and Medicaid may be affected, but in the most recent shutdown those benefits were still paid.

Crucially, services provided by individual states and municipalities rather than the federal government are not affected. So schools are open, local police and fire services function, and the majority of healthcare services operate as normal.

And Congress and the White House have protected funding so it’s business as usual there.

What services close?

Any government services not deemed essential to life and property are at risk of closure.

This includes much of the work done by government departments including Homeland Security, State, Treasury, Transportation and Justice, and dozens of government agencies like NASA, the Environmental Protection Agency, the National Weather Service and the Internal Revenue Service. This can impact a huge range of activities from food inspections and scientific research to immigration courts and business loan applications.

Federal assistance programmes like food stamps and aid to Native American communities may stop depending on the length of the shutdown.

National Parks and museums may be forced to close (unless volunteers can keep them open).

Many organisations have to operate on skeleton staff, so even where government programmes continue to operate, their scale is often restricted and bureaucratic backlogs build up.

What happens to government workers?

Government workers themselves are the worst affected. Many are required to work without pay (although they are reimbursed at the end of the shutdown). In the most recent shutdown 420,000 employees – including airport security officers, FBI agents, border patrol and prison guards and coast guards – had to turn up for work with no pay or risk losing their jobs.

Other workers are furloughed, and sent home without pay. They may or may not be reimbursed eventually depending on political will.

Independent contractors working for the government are also sent home. They are very unlikely to be paid for the lost work.

Image: Statista

In long shutdowns unpaid workers sometimes start calling in sick in large numbers, either as a protest or to find alternative work to support their families. Others have been known to rely on food banks, and Congress has passed resolutions calling on banks and mortgage providers to show leniency to federal workers in financial difficulty.

How often do shutdowns happen?

There have been 13 shutdowns since 1981, after a change in the legal interpretation of the Antideficiency Act. Most have lasted only a few days. The exceptions were in 1995/6 (21 days), 2013 (16 days), and the most recent shutdown, which at 35 days was the longest on record.

How can a shutdown end?

Both chambers of Congress and the President have to agree to start the money flowing again. Whether this involves a compromise, or one side backing down completely depends on the political landscape – in long shutdowns public opinion is usually the decisive factor.

The most recent shutdown did not end with a permanent compromise, but an agreement to reopen government temporarily while negotiations continued.

Why don’t they happen elsewhere?

Government shutdowns are uniquely American phenomena. In most parliamentary systems, a failure to pass a budget would result in the collapse of the government, and either fresh elections or the appointment of a new government. In other presidential systems, the executive has the power to overrule or dismiss the legislature if there is deadlock.

What is the fallout?

The economic cost of the most recent shutdown has been estimated at $11 billion. Although part of that is offset when the money starts flowing again, the impact on individual workers, businesses and government projects can be devastating.

The longer lasting damage can be to reputation – both to the United States as a whole, and to whichever politicians the voters choose to blame. That is the gamble that President Trump is weighing up.