Washington is gearing up for what might be an extended federal shutdown after lawmakers reached an impasse and missed the deadline to fund the government.

The Republican party backed a short-term solution to maintain government funding at current levels until Nov. 21. However, Democrats opposed it, demanding that the measure also address their healthcare concerns. They aim to overturn the Medicaid cuts implemented by President Donald Trump’s major legislation passed earlier this summer and want to extend tax credits to make health insurance more affordable for millions who purchase through the Affordable Care Act’s marketplaces.

Republicans called the Democratic proposal a nonstarter that would cost taxpayers more than $1 trillion.

Neither side shows any signs of budging.

Here’s what to know about the shutdown that began Wednesday:

What happens in the shutdown?

With funding now lapsed, the law mandates agencies to furlough their “non-excepted” staff. Employees deemed “excepted,” which include those necessary for life and property protection, continue working but do not receive payment until the shutdown concludes.

The White House Office of Management and Budget begins by notifying agencies of the funding lapse and instructs them to commence structured shutdown procedures. This notification was sent out on Tuesday evening.

The Congressional Budget Office estimates that approximately 750,000 federal workers could be furloughed daily during the shutdown, with their collective daily compensation cost estimated at about $400 million.

What government work continues during a shutdown?

A great deal, actually.

FBI investigators, CIA officers, air traffic controllers and agents operating airport checkpoints keep working. So do members of the Armed Forces.

Programs dependent on mandatory spending generally continue during a shutdown. Social Security disbursements remain unaffected. Seniors utilizing Medicare can still access doctors, and healthcare providers can receive reimbursement.

Veteran health care also continues during a shutdown. Veterans Affairs medical centers and outpatient clinics will be open, and VA benefits will continue to be processed and delivered. Burials will continue at VA national cemeteries.

Will furloughed federal workers get paid?

Yes. In 2019, Congress passed a bill enshrining into law the requirement that furloughed employees get retroactive pay once operations resume.

While they’ll eventually get paid, the furloughed workers and those who remain on the job may have to go without one or more of their regular paychecks, depending upon how long the shutdown lasts, creating financial stress for many families.

Service members would also receive back pay for any missed paychecks once federal funding resumes.

Will I still get mail?

Yes. The U.S. Postal Service is unaffected by a government shutdown. It’s an independent entity funded through the sale of its products and services, not by tax dollars.

What closes during a shutdown?

All administrations get some leeway to choose which services to freeze and which to maintain in a shutdown.

The first Trump administration worked to blunt the impact of what became the country’s longest partial shutdown in 2018 and 2019. But on Tuesday, Trump threatened the possibility of increasing the pain that comes with a shutdown.

“We can do things during the shutdown that are irreversible, that are bad for them and irreversible by them,” Trump said of Democrats. “Like cutting vast numbers of people out, cutting things that they like, cutting programs that they like.”

Each federal agency develops its own shutdown plan. The plans outline which workers would stay on the job during a shutdown and which would be furloughed.

In a provocative move, the White House’s Office of Management and Budget has threatened the mass firing of federal workers in a shutdown. An OMB memo said those programs that didn’t get funding through Trump’s mega-bill this summer would bear the brunt of a shutdown.

Agencies should consider issuing reduction-in-force notices for those programs whose funding expires, that don’t have alternative funding sources and are “not consistent with the President’s priorities,” the memo said.

That would be a much more aggressive step than in previous shutdowns, when furloughed federal workers returned to their jobs once the shutdown was over. A reduction in force would not only lay off employees but eliminate their positions, which would trigger another massive upheaval in a federal workforce that’s already faced major rounds of cuts due to efforts from the Department of Government Efficiency and elsewhere in Trump’s Republican administration.

What agencies are planning

— Health and Human Services will furlough about 41% of its staff out of nearly 80,000 employees, according to a contingency plan posted on its website.

As part of that plan, the Atlanta-based Centers for Disease Control and Prevention would continue to monitor disease outbreaks, while activities that will stop include research into health risks and ways to prevent illness.

Meanwhile, research and patient care at the National Institutes of Health would be upended. Patients currently enrolled in studies at the research-only hospital nicknamed the “house of hope” will continue to receive care. Additional sick patients hoping for access to experimental therapies can’t enroll except in special circumstances, and no new studies will begin.

At the Food and Drug Administration, its “ability to protect and promote public health and safety would be significantly impacted, with many activities delayed or paused.” For example, the agency would not accept new drug applications or medical device submissions that require payment of a user fee.

— National Park Service: As the shutdown neared, the National Park Service had not yet said whether it will close its more than 400 sites across the U.S. to visitors. Park officials said Tuesday afternoon that contingency plans were still being updated and would be posted to the service’s website.

Many national parks including Yellowstone and Yosemite stayed open during a 35-day shutdown during Trump’s first term. Limited staffing led to vandalism, gates being pried open and other problems including an off-roader mowing down one of the namesake trees at Joshua Tree National Park in California.

— Smithsonian Institution: In the event of a government shutdown, our museums, research centers, and the National Zoo will remain open through at least Monday, Oct. 6.

Impact on the economy

Phillip Swagel, director of the Congressional Budget Office, said a short shutdown doesn’t have a huge impact on the economy, especially since federal workers, by law, are paid retroactively. But “if a shutdown continues, then that can give rise to uncertainties about what is the role of government in our society, and what’s the financial impact on all the programs that the government funds.”

“The impact is not immediate, but over time, there is a negative impact of a shutdown on the economy,” he added.

Markets haven’t reacted strongly to past shutdowns, according to Goldman Sachs Research. At the close of the three prolonged shutdowns since the early 1990s, equity markets finished flat or up even after dipping initially.

A governmentwide shutdown would directly reduce growth by around 0.15 percentage points for each week it lasted, or about 0.2 percentage points per week once private-sector effects were included, and growth would rise by the same cumulative amount in the quarter following reopening, writes Alec Phillips, chief U.S. political economist at Goldman Sachs.

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Associated Press writer Ali Swenson, Fatima Hussein, Matthew Brown and Annie Ma contributed to this report.