It costs money to run the government, and it’s Congress’s job to manage the purse strings.

With the government now in the midst of its third shutdown under President Donald Trump’s leadership — the longest in US history — there’s no sugarcoating it: One of the legislative branch’s most basic functions has broken down.

Congress has let funding for federal agencies lapse again because the president is demanding funding for a southern border wall, a pet project that doesn’t have enough support in Congress to pass.

Hundreds of thousands of federal employees are going unpaid. Basic government functions, like maintaining national parks or inspecting the national food supply for disease, have been halted or dramatically reduced. Funding for key safety nets, like food aid, will run out in a couple of months.

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The Constitution gives Congress the “power of the purse” — the ability to tax and spend money for the federal government, in large part to ensure that the executive branch didn’t spend money willy-nilly. But Trump is running the show, threatening to veto spending bills that don’t reflect his hardline immigration agenda. So far, Republicans are standing behind him and Democrats are in lockstep against him.

In an age of divided government, when Democrats and Republicans are more polarized than they’ve ever been, government spending is perhaps the most bipartisan exercise Congress is tasked with. So far, they’re stuck.

Vox asked audience members on Twitter and Facebook for their questions on the shutdown. Below are answers to some of those questions.

1) What is a government shutdown?

Under the Constitution, Congress is supposed to periodically pass bills that approve spending for the federal government. In practice, those spending bills can last a few weeks or months or a whole year; they can fund the full government or just parts of it.

Whenever the current spending bill expires, lawmakers must pass a new one to keep the government running. Usually they do, but occasionally they don’t: 20 times in the past 40 or so years, the government has shut down, though most of those happened in the 1970s and ’80s.

Anyway, without an approved spending plan, the federal government starts to shut down.

The government agencies that lack approved funding suspend their operations. The agencies close up, they stop providing services, and their workers are either furloughed or forced to work without pay — which leads to a lot of them calling off work.

Now, the entire government never shuts down — major programs like the military, Medicare, and Social Security are considered mandatory spending and they keep chugging along even if there is an impasse in Congress. But the rest of the government depends on these periodic spending bills to continue operating.

2) How did the shutdown happen this time?

On December 21, 2018, Congress let funding for roughly 25 percent of the federal government expire. By the midnight deadline, the House and Senate still had not passed a spending bill appropriating money to nine federal agencies, and the government partially shut down — as it remains today.

Government shutdowns are usually the result of a stalemate in Congress. But this partial shutdown has almost nothing to do with policy disagreements in the halls of the Capitol building — and everything to do with President Trump.

The impasse comes down to Trump’s demand for $5 billion to start building a wall at the southern border, something Democrats refuse to support. Trump has asked for wall funding since he took office, but every time Congress came around to negotiating spending bills, Republicans conceded the wall in exchange for funding other priorities.

In the weeks leading up to the December 21 deadline, it looked like Republicans and Democrats would do the same. The Senate passed a spending bill that fully funded the government but didn’t touch the border wall (instead, it included $1.3 billion for border security more generally), which had enough support to pass in the then-Republican-controlled House. But Trump said he would veto that bill, so the House, then led by Speaker Paul Ryan, passed a spending bill with $5.7 billion in wall funding with only Republican votes, which the Senate would never be able to pass, upending negotiations and leaving the government to shut down.

Since then, the new Democratic House majority has passed the 2018 Senate bill to reopen the government that doesn’t include funding for the wall, but the new Senate, which is still controlled by Republicans and is heeding Trump’s demands, won’t take up that bill again.

Congress is stuck. Democrats say they won’t negotiate a wall or border security until Trump reopens the government. Trump isn’t backing down, even threatening to declare a national emergency and re-appropriate military funding for the border by fiat (he put that idea on hold). And Republicans are sitting idle.

Welcome to the longest government shutdown in US history.

3) What government programs are affected by this shutdown, and when?

A wide swath of the government is already feeling the pain of the shutdown in myriad ways: Aid to farmers affected by the Trump administration’s tariffs is facing delays, reviews for IPOs and mergers are being put on hold, and immigration cases could get postponed for years. Key services that have been affected include staffing at national parks — which have remained open but are getting trashed, and Environmental Protection Agency inspections of places like oil refineries and power plants, which have been put on pause.

Nine out of 15 federal departments and a number of agencies are affected by this shutdown, including the EPA, the IRS, and the departments of State, Housing and Urban Development, Treasury, Agriculture, Commerce, Interior, Justice, and Homeland Security. Congress has fully funded the military (aside from the US Coast Guard) and the departments of Veterans Affairs, Labor, Education, and Health and Human Services.

Each affected department, and the agencies within them, have their own contingency plans on how to handle the shutdown. They deem which employees are “essential” — and have to work without pay — and “non-essential,” which means they can be furloughed (or sent home without pay).

At DHS, for example, the majority of workers, including Border Patrol, remain on the job, while most workers at the IRS and the EPA have been sent home without pay.

If the shutdown keeps going, these effects are only expected to get more dire.

The USDA has said that food stamps will be funded through February, but it’s unclear if the agency will have the funds to keep the program going beyond that point. There have also been concerns that the IRS could struggle with this year’s tax season, the first to implement Republican tax reforms, even though the Trump administration has said that refunds will still be processed in a timely manner.

Not everything stops operating during a government shutdown. The military, air traffic control, federal prisons, and Social Security, Medicare, and Medicaid are set to keep on running.

4) So who’s to blame for this shutdown?

Most government shutdowns result in endless blame games. But in this case, Trump has actually gone on the record claiming responsibility. In a meeting with the Democratic leaders ahead of the spending deadline, he said he would be happy to shut down the government in a bid to force lawmakers to fund his southern border wall.

“I am proud to shut down the government for border security,” Trump told Democratic leaders a little more than a week before the latest shutdown started.

In December, at the last minute, the president pulled his support for a spending plan that had already passed the Senate, precipitating the shutdown. The American public accordingly blames him for the impasse far more than they blame Democrats in Congress.

As a general rule, if you are the one demanding a policy change in exchange for funding the government, rather than agreeing to keep the government open while you try to get what you want on the policy, you are responsible for shutting down the government. Today, that’s Trump. He wants the border wall in exchange for opening the government.

Republican leaders could pass a spending bill anyway, even in the face of Trump’s veto threat. Democrats believe there are the votes to pass a bill reopening the government and even to override Trump’s veto if necessary. But Senate Majority Leader Mitch McConnell has refused to move a spending bill that doesn’t have Trump’s endorsement.

The better question might be whether it matters who’s responsible. Republicans in Congress shut down the government in 2013 in a futile attempt to stop Obamacare, and voters punished them in 2014 by ... handing them a shiny new Senate majority. Democrats shut down the government for a few days in early 2018 over the Deferred Action for Childhood Arrivals (DACA) program, and the price they had to pay was... winning a House majority in the midterms.

There simply isn’t much evidence that voters hold grudges about shutdowns; they might see it as a general sign of dysfunction in Washington, but it’s not their top issue when they go to the polls.

Then again, this is now our longest government shutdown in history. We’re in uncharted territory.

5) How long can a government shutdown last?

The government reopens when Congress passes a spending bill to fund the government and Trump signs it into law. It can go on indefinitely. (Trump has even quipped that this could last months or even “years.”)

It’s unlikely that it would go on that long, in large part because shutdowns have real effects on people’s lives and the political pressure will eventually overcome lawmakers. It is worth noting, however, that come September 30, 2019 — the end of this fiscal year — the spending bills for the parts of the government that are currently funded will expire.

For now, the government is still partially shut down because of two disagreements.

One is a longstanding policy fight over border security, and the other is a negotiation over when to reopen the government. The impasse ultimately comes down to a difference in priorities. Trump wants a border wall before he will reopen the government; Democrats want Trump to reopen the government before they talk border security.

There are three ways this can end:

Trump caves, agreeing to reopen the government without funding the border wall. Democrats cave, agreeing to some — or all — of the border wall funding Trump wants and vote for a spending bill. Republicans cave and band together with Democrats, pass a spending bill with a veto-proof majority to fund the government without Trump’s approval.

It’s important to remember that government spending fights, like most bipartisan negotiations, are about political parties exercising their leverage. It’s a game of chicken, where both parties are on a collision course that ends in a painful government shutdown. In the end, someone has to give in.

6) What about all the federal employees and contractors who aren’t getting paid? What are their rights?

As of this past Friday, roughly 800,000 federal employees have missed their first paycheck. About 380,000 employees have been furloughed and another 420,000 are currently working without pay. Congress has already passed a bill that guarantees all federal employees back pay once the shutdown is over, but that does little to help them while it drags into its fourth week.

What’s more, thousands of federal contractors are potentially affected by the shutdown as well. As many as 500,000 contractors are affiliated with the agencies that are caught up in the shutdown, according to NYU professor Paul Light. Many of these contractors won’t receive any back pay at all, while others might not see any impact on their paychecks, depending on how their employers have negotiated their contracts.

Interestingly, federal employees can’t use strikes to protest the current situation. Because of the Taft-Hartley Act, which was passed in 1947, it is actually illegal for federal employees to strike, and many unions have urged their members to refrain from doing so. As Quartz points out, the impetus for the law was to deter federal employees from disrupting key government services by striking to attain better wages. It probably didn’t consider that workers would strike because they weren’t being paid for their services at all, the Atlantic notes.

Workers who don’t go into the office because they are participating in a strike could be considered “absent without leave,” the American Federation of Government Employees’ policy director Jacque Simon told the Atlantic. As a result, they could face penalties at work including, potentially, losing their jobs.

They do have some recourse, however.

The American Federation of Government Employees has filed a class-action lawsuit against the Trump administration, noting that it’s illegal to keep workers on the job without compensation. It won a similar challenge after the shutdown in 2013, ultimately guaranteeing workers who participated in the suit twice the back pay they were owed.

7) How many times has the government shut down in the past?

The government has shut down 21 times since 1976, the same year the modern budgeting process for the federal government went into effect. Since then, only one president — George W. Bush — has made it all the way through his term with no shutdowns.

Shutdowns started occurring frequently under President Jimmy Carter; five shutdowns happened while he was president. Under Carter, government agencies operated on a shoestring budget during shutdowns but didn’t actually cease to function until after 1980, when then-Attorney General Benjamin Civiletti issued legal opinions finding that in order for the federal government to not violate the 1884 Antideficiency Act, agencies truly had to shut down.

The most government shutdowns under any one president happened during the term of President Ronald Reagan. There were eight shutdowns under his tenure, but they were relatively short, lasting one to three days.

Until Trump’s most recent shutdown, the record-holder for longest shutdown was the second shutdown under President Bill Clinton, which lasted for 21 days when Clinton and congressional Republicans couldn’t agree on a spending bill.

And Trump has had three shutdowns on his watch so far: a shutdown in January 2018 over immigration and spending, an extremely short government shutdown in February 2018 after Sen. Rand Paul (R-KY) got mad about government budget caps, and the current 24-days-and-counting shutdown ... which, again, is over immigration.

8) Do other developed countries have government shutdowns?

Government shutdowns are uniquely American. When the government shuts down in the US, the people who often feel the pain are government workers going without paychecks or those who depend on affected federal programs like food stamps. In other developed countries like Australia, politicians are the ones who feel the brunt of a shutdown. For instance, the Australian parliament risks being dissolved if government isn’t funded, which, in theory, makes it less likely to happen.

“We cannot find another democracy that shuts itself down,” House Majority Leader Steny Hoyer told reporters this week. Referencing parliament dissolving itself in Australia, Hoyer quipped that it “would not be a bad alternative.”

Other developed nations also have a lower threshold for passing budgets — a budget typically needs a simple majority rather than the higher percentage required in the US Senate. Simple majorities help prevent this kind of gridlock, but they could also carry the risks of making budgets more partisan documents, since you need fewer people to pass them.

There aren’t a lot of situations comparable to the current government shutdown in Europe and other developed nations; Northern Ireland came close to the government shutting down late last year, before Great Britain intervened (Northern Ireland is part of the UK). But many other governments are designed to not hamstring government operations if the legislature fails to appropriate money.

9) This is now the third time the government has shut down in one year. Why does this keep happening?

It’s not unusual for government spending fights to go down to the wire. The budget and appropriations process is a difficult bipartisan exercise that requires Democrats and Republicans to make serious concessions on the policy priorities. (And Congress is really good at procrastinating, leaving very little time to smooth over last-minute issues.)

Congress’s failure to keep this process going three times in one year paints a very clear picture of the current political landscape.

The first shutdown under Trump happened in January 2018 because of the White House’s immigration agenda; progressive activists urged Democratic lawmakers to use their leverage in the spending fight to get assurances that Congress would protect the undocumented immigrants thrown into legal limbo after the Trump administration attempted to sunset DACA.

The second shutdown came a month later, in February 2018. Rand Paul was angry over a deal negotiated by congressional leaders that busted government budget caps in place since 2013. He held up the voting process in the final hours and left funding to lapse just overnight, to send a political message about government spending.

The current shutdown — which Trump has been threatening for months — is over the border wall, a campaign promise Trump made in 2016 as part of a fearmongering anti-immigration agenda.

Throughout history, government shutdowns have highlighted periods of intense division in policy, whether over debt management in the 1990s or funding the Affordable Care Act in 2013. But it’s important to note that the political calculus of a government shutdown has shifted over time. Shutdowns were once seen as a complete disaster. Now they’ve become part of political strategy.