WASHINGTON — The White House and Congress failed to reach a deal on funding the federal government, leading to a partial shutdown that began early Saturday. What happens now? Here’s what you need to know.

Why is there a shutdown again?

The government was operating on a stopgap funding bill that passed on Dec. 21, which followed a separate stopgap bill that passed in September. But that funding legislation expired on Saturday, and the White House and Congress remain at an impasse. The biggest dispute, though not the only one, is how to address the status of roughly 700,000 undocumented immigrants granted legal protection and work permits under President Obama that the Trump administration plans to revoke. Republicans control the House and Senate, but they need 60 votes in the Senate to pass a bill (there are only 51 Republicans). House Republicans passed a bill on Thursday to fund the government through February 16 that did not include an immigration deal, but Senate Democratic leaders opposed the short-term bill and some Republicans voted against it as well.

What happens now they didn't find a deal?

We have a partial government shutdown. While funding expired on Saturday, you’ll really start to notice the effects on Monday when hundreds of thousands of federal employees who are deemed non-essential don’t show up to work. Without funding, the law requires them to be furloughed without pay. In 2013, the last time there was a shutdown, a peak of 850,000 federal workers per day were furloughed, according to the Congressional Research Service, which added up to about 40 percent of the total federal civilian workforce.

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Without workers, various government offices, programs, and activities would be shut down. Affected agencies could include the Centers for Disease Control and Prevention, the Internal Revenue Service, and numerous civilian workers at the Department of Defense. Congress will still go to work to try and reach a solution, but much of their staff will be staying home.

Some services that have a separate funding stream will stay open. The mail would still be delivered. Federal courts could operate for a short time using various fees they’ve collected, but might have to furlough some staff while others work without pay, especially if the shutdown continues for an extended period.

There could be some differences between this new shutdown and the last one. White House budget director Mick Mulvaney said Friday that national parks, which were closed during the 2013 standoff, would stay open, but nobody will be picking up the trash during the shutdown.

This whole shutdown process is a relatively recent phenomenon. The government used to keep more services up and running during funding gaps, but the Department of Justice decided in 1980 and 1981 that existing law demanded a more far-reaching shutdown if Congress failed to pass a spending bill.

Who’ll be guarding the country?

Here’s where the “partial” in partial government shutdown kicks in. Federal workers considered essential to national security and the safety of life and property will still have to show up and do their jobs. That includes the military, law enforcement officials, TSA screeners, doctors, border patrol agents, firefighters, meat and poultry inspectors, and air traffic controllers, among others.

Despite showing up for work, the excepted workers will not get paid unless Congress authorized more funding.

This doesn’t mean the shutdown won’t be disruptive either. Secretary of Defense James Mattis warned in an appearance at Johns Hopkins University on Friday that training exercises for reservists and maintenance of weapons systems would be delayed and there would be “a huge morale impact” across the board.

It’s possible lawmakers might take steps to remove members of the military and other defense workers from the shutdown fight, though. In 2013, Congress passed the Pay Our Military Act, which ensured paychecks for the military would continue during the shutdown and also allowed hundreds of thousands of civilian defense workers who would otherwise be furloughed to keep going to work as well. But that law was not permanent, and Congress would have to pass a similar bill this time if they want to pay the same service members, federal employees, and contractors during the shutdown.

What about government benefits?

Social Security, which has its own funding source, will issue its usual checks. Medicare and Medicaid should still be able to pay out benefits. It’s possible customer service and various administrative duties might be impacted by furloughed employees, however. Death benefits for families of fallen soldiers would not be paid out, an issue that the administration resolved in 2013 by partnering with a private charity to pay them out instead and be reimbursed later.