Even as the National Rifle Association (NRA) has been consumed by relentless and increasingly public infighting, Wayne LaPierre has maintained a firm grip on its leadership.

Now one of the gun group’s major benefactors says he is preparing to lead an insurgency among wealthy contributors to oust Mr LaPierre as chief executive, along with his senior leadership team.

Such a rebellion would represent a troublesome new threat to Mr LaPierre, as his organisation’s finances and vaunted political machine are being strained amid a host of legal battles, most notably the New York attorney general’s investigation into its tax-exempt status.

David Dell’Aquila, the restive donor, said the NRA’s internal warfare “has become a daily soap opera, and it’s decaying and destroying the NRA from within, and it needs to stop”.

He added, “Even if these allegations regarding Mr LaPierre and his leadership are false, he has become radioactive and must step down.”

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Until that happens, Mr Dell’Aquila, a retired technology consultant who has given roughly $100,000 (£80,000) to the NRA in cash and gifts, said he would suspend donations — including his pledge of the bulk of an estate worth several million dollars.

He said he was among a network of wealthy NRA donors who would cumulatively withhold more than $134 million (£106 million) in pledges, much of it earmarked years in advance through estate planning, and would soon give the gun group’s board a list of demands for reform.

That figure could not be verified, however, and Mr Dell’Aquila declined to provide a list of the other donors, who he said were not ready to go public.

But a second prominent donor, who spoke on the condition of anonymity because he is a senior firearms industry executive, said he was also suspending a plan to give more than $2 million (£1.6 million) from his estate, as well as halting other donations, and was backing Mr Dell’Aquila’s effort.

“The donors are rebelling,” the executive said, adding that he believed that the leadership turmoil was “helping to destroy, temporarily, the strength of the NRA as one of the strongest lobbying groups”.

The extent of any rebellion is difficult to discern, and the NRA insisted it still had the firm backing of its donor base.

Mr LaPierre has also retained the support of the NRA’s 76-member board, with fewer than a handful of public defections, and it would take a three-fourths vote by the board and one of its committees to oust him.

But there have been signs of wavering grassroots support, including a recent announcement by Greg Kinman, a gun enthusiast with more than 4 million followers on YouTube, that he was cutting ties with the NRA.

The turmoil of recent months has already stoked fear among some Republicans that the NRA’s political potency could be blunted heading into the 2020 elections.

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In a tweet early on Tuesday morning, President Donald Trump assailed the investigation by the New York attorney general, Letitia James, saying the NRA was “a victim of harassment by the AG”.

Carolyn Meadows, the NRA’s president, said in a statement that “we are disappointed whenever donors choose to suspend their support of the NRA, but we hope to win them back.”

She added: “People may resist change, but they embrace progress. We’re experiencing that right now at the NRA. There’s an energy within the NRA. that is hard to describe — and we continue to earn the support of millions of loyal members.”

The support of donors and the enthusiasm among NRA members will be a crucial test for Mr LaPierre, who has led the organisation for more than two decades.

Last month, Mr LaPierre ousted his second-in-command, Christopher W Cox, who led the gun group’s lobbying arm; in April, the NRA’s president, Oliver North, abruptly stepped down.

Both men have been implicated by the NRA in a plot to force Mr LaPierre out, though Mr Cox has denied the allegations. Mr North has said the NRA needs to review its financial practices; NRA officials have said the split with Mr North was largely a dispute over money.

Both Mr Dell’Aquila and the second donor want Mr Cox to return to the NRA and become its chief executive.

“He brings continuity and stability,” Mr Dell’Aquila said, adding that Mr Cox had emerged from the recent wave of scandals with cleaner hands than Mr LaPierre. “We can get consensus with Chris replacing Wayne.”

Mr Dell’Aquila said he had not spoken to Mr Cox about the matter and had not seen him since a fundraiser last year.

The NRA is moving on from Mr Cox and is expected to announce on Tuesday that Jason Ouimet, a deputy at its lobbying arm, will assume Mr Cox’s former post, according to a person with knowledge of the appointment.

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The NRA has been burdened by high structural costs and escalating legal bills as it copes with the New York investigation and a bitter legal fight with its former advertising firm, Ackerman McQueen.

The NRA’s member dues fell in 2017 to their lowest level in a half-decade, as concerns about gun control ebbed after Trump’s election, but they rebounded last year, increasing by a third, to $170 million (£135 million), while contributions grew by 24 percent to $165 million (£130 million).

Even so, the NRA’s net assets fell sharply last year, and the organisation was forced to freeze its pension fund.

It also took more than $30 million (£23.8 million) out of its charitable foundation in 2017; it recently increased a line of credit, backed by the deed to its headquarters, to $28 million (£22 million); and it borrowed against life insurance policies taken out on top executives.

In a series of interviews and emails, Mr Dell’Aquila cited numerous concerns.

He was troubled that a former NRA president, David Keene, had been caught up in an investigation over his ties to Maria Butina, the Russian who pleaded guilty to conspiring to act as a foreign agent.

He was disturbed after The New York Times reported this year that Tyler Schropp, a senior NRA executive, had an interest in an outside company that had received $18 million (£14 million) from the NRA.

He was also dismayed by a recent New Yorker story tying the NRA’s former longtime chief financial officer to allegations of embezzlement at a previous job.

“I don’t know if these stories are true or not true,” he said. “My No. 1 concern, frankly only concern, is that our Second Amendment rights are preserved and the optics of negativity that are directly harming the NRA institution ceases.”

Mr Dell’Aquila said he had approached high-ranking NRA officials to express his dissatisfaction as recently as April, when the NRA held its annual convention in Indianapolis, but was not satisfied by their responses.

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And he said the board had recently been removing critics of LaPierre from key oversight committees.

“I decided the best way to be effective is to start a grassroots effort to demand from the NRA leadership accountability as well as transparency,” he said.

His demands include the resignation of Mr LaPierre and his senior leadership in time to put in a new team for the 2020 elections.

In addition to Mr Cox’s return, he wants Allen West, an NRA board member and former Tea Party congressman opposed to Mr LaPierre, installed as the group’s president.

He would also shrink the board to 30 members from 76; stop paying consulting fees to board members; dismiss the NRA’s accounting firm, RSM; remove past presidents from the board; and cut costs by holding meetings in central locations.

He lamented that an upcoming board meeting was to be held in Alaska: “What are the optics of that?” he said. “It’s negative. It’s self-inflicted.”

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He adding that the NRA could find board members who “would do this for free, and it keeps us clean in the liberal papers”.

Mr Dell’Aquila said he had come to his decision reluctantly and had always been treated graciously by Mr LaPierre and his wife, Susan.

“I’m not pro-Mr LaPierre, and I’m not anti-Mr LaPierre, I’m just simply being objective and trying to save a historic institution from itself,” he said.

“Right or wrong, the buck stops with Mr LaPierre, because this occurred underneath his leadership, and he’s ultimately accountable.”