What is a government shutdown? Deadline for US spending bill and what happens if it is missed

America is hours away from its government grinding to a halt as Congress has yet to sign off funding to keep its national agencies and services running.

In a quirk of US politics the budget for certain departments needs to be authorised annually – and it’s looking unlikely this will happen before the 12.01am (5.01am BST) deadline on Sunday, ahead of its new financial year starting on October 1.

If the House of Representatives and the Senate cannot agree on the new spending bill for President Joe Biden to sign into law, millions of government staff, including soldiers, will not being paid.

It could also mean museums, national parks, research facilities and health centres with national government funding suspend operations.

Is it likely this will happen?

On Saturday Republican Speaker Kevin McCarthy said the House of Representatives will vote on a stopgap funding bill.

The last-minute scramble to approve spending will require Democratic votes, which will anger some party hardliners who had wanted to pass a bill without their support.

Even if the House passes the bill, there may not be enough time for the Democratic-majority Senate to vote on the measure and Mr Biden sign before Sunday.

This move will test Mr McCarthy’s narrow 221-212 majority, where hardline conservatives have opposed the idea of a short-term bill, and could lead to a challenge to his position as speaker.

How has it come to this?

The House of Representatives and the Senate are divided on where to spend part of its almost US$6 trillion budget and Mr McCarthy said he opposed $6 billion (£5 billion) in Ukraine aid.

Infighting among Republicans who control the House by a 221-212 margin has pushed the US to the brink of its fourth partial shutdown in a decade, as the chamber has been unable to pass legislation that would keep the government running.

What departments will shut down?

Government agencies have already drawn up detailed plans that spell out what services must continue, like airport screening and border patrols, and what must shut down, like scientific research and nutrition aid to seven million poor mothers.

Most of the government’s four million-plus employees would not get paid, whether they were working or not.

The impact would also hit millions of Americans who will rely on government assistance. They will also experience delays in services.

Has this happened before?

The US has a history of government shutdowns. There were more in the 1980s and 1990s – this will be the fourth in a decade.

The last shut down from 2018-19 was over Donald Trump’s demand for $5.7 billion (£4.7 billion) to build the Mexican wall.

How long will this shutdown last?

It could be days or even weeks before it is resolved. A prolonged shutdown could also affect the US food stamp programme that serves 40m low-income Americans, and impact the implementation of a new scheme to serve free breakfast and lunch to students in high-need school districts.

Additional reporting by Reuters