Washington, DC - Republicans scrapped plans for a vote Wednesday on a funding deal to thwart a damaging US government shutdown amid a growing rank-and-file rebellion that threatened efforts to keep the lights on through the presidential election.

Government funding is set to expire at the end of September and Congress will need another stopgap bill – known as a "continuing resolution" (CR) – to keep operations open past the election because the parties are nowhere near agreement on a full-year budget.

Former president Donald Trump has urged Republicans to force a shutdown unless certain demands are met.

A US government shutdown would cause the closure of federal agencies and national parks, limiting public services and furloughing millions of workers without pay just weeks before the election.

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Republican House Speaker Mike Johnson had planned to call a vote later Wednesday on a six-month extension, punting the shutdown deadline into March, when the next president would be in office.

He announced that he intended to pair it with legislation requiring proof of citizenship when registering to vote in federal elections, known as the SAVE Act.

But he called off the vote around midday as it became increasingly clear how unpopular the plan was with members from all sides of his party, and that he could not rely on Democratic votes.

Johnson said he still plans to lobby Republican support for the bill in the hope of turning around some of the dissidents.

Trump, who dominates the House Republican group and continues to claim falsely that he was cheated by voter fraud in the 2020 election, has lobbied for Johnson to add the election measure to the funding package.

"I would shut down the government in a heartbeat... if they don't get it in the bill," Trump told Monica Crowley, a senior Treasury official in his administration, on her podcast.

President Joe Biden's administration – worried about eligible voters being blocked from voter rolls or otherwise deterred – opposes the SAVE Act, noting that noncitizen voting is already illegal and that there is no evidence that it happens.

Johnson was unable to win the support of a critical mass of his own side – despite warning that he would have no fallback option if the package failed – risking a shutdown at the start of October, less than five weeks before Election Day.

"We're going to continue to work on this. The whip is going to do the hard work and build consensus. We're going to work through the weekend on that," Johnson said as he announced the funding vote would be postponed.

In the Senate, the governing Democrats plan to strip the voting provisions and give Republicans in the House an ultimatum: pass a "clean" CR moving the funding deadline to the end of the year or trigger a government shutdown.

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With the election less than two months away, vulnerable Republicans see a government shutdown as disastrous for their reelection prospects.

At least 10 lawmakers from all sides of the party came out against the Johnson proposal – although the real number of Republican dissidents is thought to be larger – with defense hawks worried about military readiness and fiscal conservatives always against stopgap funding measures that do not cut spending.

Republicans can only afford to lose four members on any party-line vote.

The spending fight is Johnson's last big test before he asks his lawmakers for another two years at the helm.

He has argued that a March funding deadline would allow an incoming president Trump to weigh in on spending if he wins the White House, rather than approving the funding under a lame-duck Biden.