It’s official. The government has partially shut down — thanks to Trump’s demands for $5 billion in border wall funding.

While much of the government remains open, a portion has now gone into shutdown mode, including the Department of Homeland Security, the State Department and the Justice Department.

The root of the partial shutdown is a contentious fight over funding for the border wall: Barring Trump’s assurances that he would pass a temporary spending package without this funding, House Republicans refused a Senate option that didn’t include it and instead approved their own bill, which the Senate rejected.

As of early Saturday morning, when government funding ran out for a slew of federal agencies, the two chambers have yet to approve a version they both like.

The good news is that most of the government was funded earlier this year. Congress has already approved funding for 75 percent of the government with other appropriations bills, meaning key agencies like the Departments of Education and Health and Human Services have secured their appropriations and aren’t affected by this shutdown at all.

It’s entirely unclear how long this shutdown will last — though, in one scenario, it could go as long as January 3 when control of the House shifts to Democrats. Some lawmakers have also suggested that it could get resolved as soon as this weekend. Senators said Friday that they were interested in considering a deal that would satisfy both chambers, as well as the President, which could mean an agreement that includes $1.6 billion in border security funding.

Many government agencies operate with a skeleton crew over the holidays, but if the fight drags on longer, it could start to significantly impact government functions. This is actually the third government shutdown this year, and with a Democratic majority coming into the House in January, there may be more to come.

This shutdown threat is all about Trump

There’s not a lot of gray area about the central cause of the shutdown. Trump preemptively and explicitly took the credit for the shutdown during an explosive Oval Office meeting with House Minority Leader Nancy Pelosi and Senate Majority Leader Chuck Schumer last week.

“I am proud to shut down the government for border security, Chuck. … I will be the one to shut it down. I’m not going to blame you for it,” Trump said at the meeting, dashing any Republican hopes of using Democrats as their cover.

But he changed course at the last minute this week — putting the shutdown on Democrats in a tweet on Friday.

This is far from the first time Trump has said he’d veto a spending bill over the border wall but this time he was serious. Many wondered why he decided to pick this fight now, while Republicans still control both chambers of Congress rather than wait to go up against a Democrat-controlled House, when he could effectively shift the blame.

Part of this calculus is that a Republican-dominated House is much more likely to help Trump get closer to what he wants. Another reason might be related to the fact that Republican voters aren’t too troubled by the possibility of a shutdown as long as it’s the result of Trump standing his ground.

While government shutdowns have historically been viewed as wasteful and a poor reflection on elected leaders, a recent Marist poll found that 65 percent of Republicans were open to a shutdown if it meant that Trump didn’t compromise on a border wall, The Washington Post reports.

Who is affected by the shutdown

Depending on the duration of the partial shutdown, hundreds of thousands of federal employees could be furloughed, while some federal agencies will limit the services they provide.

Since this is a partial shutdown, only agencies that fall under the parts of the government that have yet to be funded will see any impact.

Because National Parks are overseen by the Department of Interior, which is still waiting on funding, they could experience limited operations even though many are likely to remain open, for example. Other services like veterans benefits will not observe any effects because these programs were already funded earlier this year.

Additionally, mandatory programs including Medicare are due to keep running, though new sign-ups could see some delay.

There’s also a somewhat confusing political twist in this partial shutdown.

Among the slew of “essential” government workers who will keep working, despite the shutdown, are active duty members of the military as well as the majority of those working in U.S. Customs and Border Protection, including border patrol.

Both groups are on deck to continue reporting to work over the holidays, though they won’t receive their backpay until the government officially reopens. Ironically, this would mean that Trump is basically calling on both border patrol and members of the military, to spend the holiday season working without immediate pay.

“If a lapse in appropriations were to take place, a majority of DHS activities would continue,” an administration official told CNN. “For instance, those protecting our borders with the Customs and Border Patrol will continue to do so.”

What and who will keep working

• Social Security, Medicare and Medicaid
• United States Postal Service
• Veterans hospitals and benefits
• Food stamps (The agency has limited funds, but the programs will continue operating in the short-term.)
• Active duty military
• Border patrol
• Air traffic control and TSA

What will be closed or could see limited operations

• National Parks
• The IRS and tax refunds
• State Department services (Passports and visas will continue to be issued though some services could be closed.)
• Environmental and food and drug inspections

What happens now?

While there’s still an apparent chasm between Democrats and Republicans, lawmakers are able to end the shutdown by inking some kind of agreement on the outstanding spending bills.

As Golshan and Scott have noted, they have a couple different options at their disposal:

[They] can 1) pass the appropriations bills, likely in an minibus, which just crams together [7] appropriations bills into one spending package; 2) pass a “continuing resolution” (CR), which would fund the government at its current levels, basically buying more time to negotiate the actual appropriations bills; or 3) pass a “CRomnibus,” which is a combination of the two, extending the deadline on certain more contentious appropriations — like for the Department of Homeland Security — and passing a spending bill on the rest.

Earlier this week, lawmakers seemed close to averting a partial shutdown after the Senate passed a continuing resolution that would keep the government fully funded through February 8th. A vocal contingent of House Republicans were displeased with this option, however, and urged Trump to maintain his opposition — something which he clearly has.

Until Trump and lawmakers agree on a new deal, this partial shutdown could continue to drag on as the Christmas holiday rapidly approaches, sending this lame-duck Congress out on anything but a high note.