With just five days until the new fiscal year begins on October 1, US legislators are scrambling to overcome an impasse fuelled by hardline Republicans who have promised to block funding legislation unless deep spending cuts are made.

If no measure is passed before a midnight deadline on Saturday (04:00 GMT on Sunday), large swaths of the government will be forced to shutter with only a few essential services remaining.

On Tuesday, the administration of US President Joe Biden, a Democrat, labelled the situation an “extreme Republican shutdown”, saying it would also disrupt US national security.

“If Republicans in the House don’t start doing their jobs, we should stop electing them,” the president said earlier this week, accusing GOP lawmakers of failing to fulfil “one of the most basic fundamental responsibilities of Congress”.

Here’s all you need to know.

How did we get here?

Biden and Republican Kevin McCarthy, the speaker of the House of Representatives, had agreed in May to authorise $1.59 trillion in discretionary spending for the next fiscal year.

The agreement, relating to the amount of money Congress can allocate to various parts of the government, was meant to avert the current standoff.

However, a right-wing flank of the Republican Party has since rejected the deal, calling for a wider debate on government spending and for about $120bn to be cut from the $1.59 trillion that was previously agreed.

Several more moderate Republicans support the full amount of funding McCarthy and Biden agreed to. However, the hardliners have outsized influence in the House because the GOP only holds a 221-212 majority over Democrats.

Why do the hardliners oppose the funding legislation?

At particular issue has been including more aid to Ukraine in the funding package, with a growing number of Republicans staunchly opposed to providing more assistance to the country in its conflict with Russia.

McCarthy has publicly questioned the breadth of Washington’s continued military and humanitarian support for Kyiv in an attempt to appease the hardliners, but his efforts have come up short.

Last week, they blocked a usually popular defence bill despite the fact that it included an 8 percent cut to many services and measures to strengthen the US-Mexico border.

Republican Representative Matt Gaetz of Florida, a key ally of former President Donald Trump who is leading the right flank, told Fox News that while a government shutdown is not optimal, “it’s better than continuing on the current path that we are to America’s financial ruin.”

Gaetz also has been a vocal critic of McCarthy, threatening to remove the House speaker from his post if he tries to work with Democrats to pass a “short-term stopgap measure” to avert the shutdown, NBC News reported on Tuesday.

What would a shutdown mean?

A government shutdown means that hundreds of thousands of federal workers would be furloughed and a wide range of government services would be suspended. Government workers deemed essential would remain on the job, but would work without a paycheque.

A shutdown affects nearly every corner of the US government, from the delivery of welfare cheques and publishing of national economic data, to the operation of federal courts.

The Biden administration has warned that seven million people who rely on a federal food aid programme for women and children could see that assistance stop.

Other government services would move to contingency plans. For instance, federal airport security screeners and air-traffic control workers would be required to work, but without pay.

A message from me on the extreme Republican shutdown: pic.twitter.com/Gofyc437z6

— President Biden (@POTUS) September 26, 2023

The White House has also said that 1.3 million active duty military personnel would be at risk of not being paid, while hundreds of thousands of civilians in the Department of Defense would be furloughed.

“All of this would prove disruptive to our national security,” the White House said on Monday.

Meanwhile, Moody’s has warned that a shutdown would have negative implications for the US government’s AAA credit rating, as it would highlight how political polarisation is worsening the country’s fiscal standing.

What is being done to avoid the shutdown?

Legislators in both parties are meeting on Tuesday to find a solution, but no clear path has emerged.

The House is expected to vote on Tuesday evening on a package of bills to fund parts of the government, including the Defense, Homeland Security, Agriculture, and State departments.

But it remained unclear if McCarthy would have the needed support from his Republican Party.

“Let’s get this going,” McCarthy said after a meeting of the House Rules Committee on Saturday in preparation for this week’s voting. “Let’s make sure the government stays open while we finish our job passing all the individual bills.”

At least one top Trump ally, Representative Marjorie Taylor Greene, who is also close to McCarthy, said she would be a “hard no” on the vote to open debate, known as the Rule, because the package of bills continues to provide at least $300m for the war in Ukraine.

Even if passed, the bills would not prevent a partial shutdown.

In the Senate, where Democrats have a majority, legislators were preparing a bipartisan plan for a stopgap measure to keep offices funded past the upcoming deadline.

However, plans to tack on additional Ukraine aid could see some Republicans seek to slow-roll the passage with few days left.

Will a shutdown have any political effects?

Regardless of who forces a shutdown, they have historically proven widely unpopular for US presidents, and could be damaging to Biden’s 2024 re-election bid.

Trump, who is the current frontrunner in the Republican Party’s 2024 nomination race, has urged his allies in the House to hold a hard line.

“Unless you get everything, shut it down!” he wrote in all capital letters on his Truth Social platform on Sunday.

Trump himself forced a 35-day shutdown over border controls in 2018 but ended up reopening the government after failing to secure any concessions from Democrats.