WASHINGTON — The U.S. government will shut down this weekend unless Congress comes up with a plan and acts soon.

Federal funding expires when the clock strikes 12:01 a.m. Saturday, and congressional Republicans are back to the drawing board after billionaire Elon Musk and President-elect Donald Trump blew up their original bill and then passed it on Thursday night Replacement plan failed.

As Congress debates a path forward, the government operations people rely on and the paychecks for millions of federal workers are at stake.

Here’s what you need to know about what a government shutdown is and how it could affect you:

What is a government shutdown?

The Constitution gives Congress power over the purse strings, meaning nearly all government funding decisions are made on Capitol Hill. Every year, Congress must pass spending legislation before October 1, the start of a new fiscal year, or the government will run out of money to continue functioning.

If Congress does not take action before that date, the House and Senate can also pass legislation, called a continuing resolution, to keep the government fully functioning for a short period of time. Back in September, Congress did just that and set December 20 as the new deadline.

Now Congress must act before the end of Friday or there will be a funding shortfall. Then all non-essential government functions must cease.

How did Congress get to this point?

Here’s how the government spending process is supposed to work: The appropriations committees of both chambers are supposed to pass a dozen spending bills each year that affect various federal agencies. The bills must then pass both the full House of Representatives and the Senate before reaching the president’s desk for signing into law.

This rarely happens at modern conferences. As has become common practice, Congress ran out of time in September to complete the process and so passed a short-term funding extension.

Although Congress has known about the Dec. 20 deadline since the fall, it only this week released an agreement to avoid a shutdown.

On Tuesday evening, House Speaker Mike Johnson, R-La., announced the deal reached between top Republicans and Democrats in Congress. It would have extended federal funding through March 14 and provided economic aid to farmers and aid to hurricane-affected areas. For the first time in more than a decade, it also included a small pay increase for members of Congress of a maximum of 3.8%.

Before the House of Representatives even scheduled a vote on it, Musk began posting negative comments about the bill to his more than 200 million followers on his platform X. Trump and a number of right-wing members of Congress also spoke out against the plan. He called it a gift to Democrats and criticized some policy provisions, such as Congressional increases.

Trump also added a last-minute demand: that Congress pass legislation to address the debt ceiling. The country is not expected to hit its debt ceiling any time next year, but on Thursday Trump told NBC News he wants Congress to lift the debt ceiling entirely.

House Republicans tried to pass a second bill to address Trump’s concerns, but it failed with nearly all Democrats and 38 Republicans voting against it. Now they must find a new path as the deadline draws ever closer.

When would a shutdown begin? How long could you last?

Without short-term action from Congress, the shutdown would begin at 12:01 a.m. Saturday, meaning the effects wouldn’t be immediately felt until Monday.

It’s hard to predict how long a shutdown might last, but if it happens, it could last a while given the divisions on Capitol Hill and the upcoming holidays. Republicans have a narrow majority in the House of Representatives and Democrats control the Senate. That will change on January 3rd when Republicans take control of both chambers of Congress, and then Trump will be sworn in on January 20th.

Rep. Marjorie Taylor Greene, R-Ga., posted on X that she would support shutting down the government through Inauguration Day.

Which parts of the government would be affected by a shutdown?

During a shutdown, the federal government would be unable to pay its millions of employees, including military personnel and reservists, just before the holidays.

Hundreds of thousands of government employees could be furloughed, meaning they would temporarily stop going to work. During a shutdown in 2013, about 850,000 workers were furloughed. But even those who have to continue to perform vital tasks would not be paid for the duration of a shutdown.

Federal workers would receive retroactive pay when the government reopens, something that wasn’t always guaranteed until Congress passed a law following a shutdown in 2019.

Some government functions would continue, including the military and public safety, such as air traffic control and the Transportation Security Administration. Each federal agency creates a “contingency plan” that determines what to do during a shutdown and which employees are “exempt” from furlough.

The Defense Department, for example, would require active-duty military members to continue reporting for duty, and inpatient and outpatient emergency care at the Pentagon’s medical treatment facilities would continue during a shutdown, a defense official told NBC News.

Disbursement of retirement benefits for military retirees would continue because they come from a separate trust fund rather than congressional appropriations, but they could be slowed by a lack of staff to process them, the official said.

President Joe Biden and members of Congress would all continue to work and be paid as required by law.

Would a shutdown impact benefits and payments like Social Security?

Social Security checks that go to 73 million people in the United States each month would continue during a shutdown because it is considered “mandatory” spending and is not funded by the dozens of appropriations bills Congress is supposed to pass each year.

Other examples of mandatory spending that would continue include Medicare payments, Medicaid payments, Temporary Assistance to Needy Families and veterans benefits.

How long was the longest government shutdown?

Congress allowed funding to expire several times over the past four decades, resulting in 20 shutdowns that lasted at least a full day.

The longest shutdown was also the youngest: from December 21, 2018 to January 25, 2019, the government closed for 34 full days.

During this closure, national parks remained open, but trash piled up as park employees were furloughed. TSA employees who continued to work without pay called in sick, causing delays at airports. The TSA administrator has warned that a closure this year would lead to longer wait times ahead of the holidays.