On Wednesday, House Republican leaders faced an immediate revolt over a continuing resolution that expanded current levels of government funding until March 14 and included an additional $110.4 billion in spending. President-elect Donald Trump backed those frustrated with House Speaker Mike Johnson (R-LA), killing the continuing resolution just days before the Friday government shutdown deadline. Congressional leaders are now scrambling to make a new deal before the government is scheduled to shut down Friday at midnight.

Congress is required to pass 12 appropriations bills for every fiscal year, negotiated by Congress and signed by the president. The bills decide government spending for a full fiscal year. If the bills aren’t passed, the government has no money to function with. In the event of an inability to secure funding, the government shuts down, ending all nonessential services until Congress passes a spending bill.

The government typically classifies border protection, medical care, air traffic control, law enforcement, and power grid maintenance as essential. Military personnel must continue their duties as usual. Social welfare programs such as Social Security, Medicare, and Medicaid also continue unimpeded, according to the Committee for a Responsible Federal Budget.

These programs are able to continue as they are funded through mandatory funding bills, which aren’t voted on, as opposed to discretionary spending funded through appropriations bills.

When appropriations bills can’t be agreed upon, Congress kicks the can down the road by passing continuing resolutions, which continue government funding at its current level for an allotted period of time. The current continuing resolution would expand funding into March.

Government workers go without pay during a shutdown, including essential employees still required to work, who are paid after funding is secured.

Arlington National Cemetary, for example, continues all services throughout a shutdown, including burial services, operations, and ceremonies.

However, programs that continue throughout the shutdown are usually still affected in certain ways. With Social Security, payments are still sent to recipients, and limited services such as issuing Social Security cards and holding appointments for benefit applications will still be held. However, benefit verifications and processing overpayments will cease, along with a major increase in customer service wait times.

Travel is affected negatively, as many Transportation Security Administration agents fail to show up to work because of a lack of pay. This could spell disaster if the government shuts down after Friday, occurring during one of the busiest travel times of the year. The TSA is expecting 40 million airline travelers between Dec. 19 and Jan. 2.

While government buildings with workers deemed essential will continue their work, visitor centers will be closed, meaning federal buildings will be cut off from the public. The salaries of Congress and the president are decided in mandatory funding rather than appropriations bills, meaning they will remain working throughout the shutdown.

Each agency develops its own contingency plan for a shutdown. The Office of Management and Budget maintains a list of each plan on its website.

The percentage of workers furloughed, working without pay, and working with pay vary widely by agency. Nearly all of the roughly 450,000 Veteran Affairs workers will work with pay in the event of a government shutdown, while nearly all of NASA’s roughly 18,000 workers will be furloughed.

The government has shut down twice in the last 11 years, once in 2013 and once in 2018-2019. The latter, over a border wall funding dispute, was the longest government shutdown in U.S. history, lasting 35 days. The 2018-2019 shutdown ended in a blow for Trump, then-president, who was popularly blamed for the shutdown.

A January 2019 Washington Post-ABC News poll found that a majority of people blamed Trump and the Republicans for the shutdown, 53%, compared to 34% who blamed then-House Speaker Nancy Pelosi (D-CA) and the Democrats. Trump’s approval rating similarly declined.

Though the incumbent president usually takes the blame for government shutdowns, it’s unclear if this will be the case with the lame-duck President Joe Biden, who has been largely absent from discussions.