President Donald Trump vowed to fight for gun rights as he addressed the National Rifle Association and implored members of the group, struggling to maintain its influence, to rally behind his re-election bid.

Speaking to the gun lobby group for his third straight year, Mr Trump declared himself a “champion for the Second Amendment” and said he planned to revoke the status of the US as a signatory of the 2013 Arms Trade Treaty.

“It’s under assault,” he said of the constitutional right to bear arms on Friday.

“But not while we’re here.”

And he told the thousands in the crowd: “You better get out there and vote,” saying of the 2020 election, “It seems like it’s a long ways away. It’s not.”

Mr Trump said he intends to drop out of the treaty, signed by then president Barack Obama but was never ratified by the Senate.

“We’re taking our signature back,” Mr Trump said to the cheering attendees, many wearing red hats emblazoned with the Republican president’s “Make America Great Again” slogan.

The NRA has long opposed the treaty which regulates the $US70 billion ($99 billion) business in conventional arms and seeks to keep weapons out of the hands of human rights abusers.

THANK YOU @NRA! #NRAAM pic.twitter.com/SWkpe1eFhT

— Donald J. Trump (@realDonaldTrump) April 26, 2019

The nation’s largest gun rights organisation was pivotal to Mr Trump’s victory in 2016. But three years later, the group is limping towards the next election divided and diminished.

It’s a reversal that has stunned longtime observers and gun control advocates and raises questions about the one-time kingmaker’s clout heading into 2020.

“I’ve never seen the NRA this vulnerable” said John Feinblatt, president of Everytown for Gun Safety, a nonprofit that advocates for gun control measures.

In the months after Trump’s election, the NRA seemed on top of the world. After pouring tens of millions of dollars into the presidential race, its dark horse candidate occupied the desk in the Oval Office.

Republicans controlled both branches of congress.

And the emboldened group had ambitious plans for easing state and national gun regulations.

NRA’s power and finances under scrutiny

Instead, much of the legislation the group championed has stalled due, in part, to a series of mass shootings, including the massacre at a Parkland, Florida, high school that left 17 dead and launched a youth movement against gun violence that has had a powerful impact.

At the same time, the group is grappling with infighting, bleeding money and facing a series of investigations into its operating practices, including allegations that covert Russian agents seeking to influence the 2016 election courted its officials and funnelled money through the group.

As Mr Trump landed in Indianapolis, a judge imposed an 18-month prison term on gun rights activist Maria Butina, an admitted Russian agent who tried to infiltrate American conservative groups.

And then there’s the simple fact that, with Mr Trump in office, gun owners no longer fear the Second Amendment is under attack.

The NRA, said Adam Winkler, a UCLA law professor and expert on gun policy, has also dramatically changed its messaging over the past two years, with its NRATV service advocating a panoply of far-right political views that have turned off some members.

At the same time, public sentiment has shifted.

A March AP-NORC poll found that 67 per cent of Americans overall think gun laws should be made stricter – up from 61 per cent in October 2017.

And a June 2018 Gallup poll found overall favourable opinions of the NRA down slightly from October 2015, from 58 per cent to 53 per cent.

Unfavourable views have grown, from 35 per cent to 42 per cent.

Against that backdrop, Democratic politicians have become more comfortable assailing – and even actively running against – the NRA and pledging action to curb gun violence.

And gun control groups like Everytown, which is largely financed by former New York City mayor Michael Bloomberg, and a political action committee formed by Gabby Giffords, the former Arizona congresswoman wounded in a shooting, have become better organised and more visible, especially at the state level.

That reversal was made clear during the 2018 midterm elections, when those groups vastly outspent the NRA.

During the midterms, the NRA “committed almost a disappearing act”, said Everytown’s Feinblatt.

Mr Winkler allowed that the group had scored some victories under Mr Trump, including the appointment of two Supreme Court justices who may be open to striking down gun laws.

But overall, he said, “On the legislative front, the NRA has been frustrated,” with top priorities like national reciprocity for conceal carry laws and a repeal of the ban on silencers stalled.

Instead, Mr Trump introduced a new federal regulation: a ban on bump stocks after a man using the device opened fire on a crowd of concertgoers on the Las Vegas strip in Nevada, killing 58 people and wounding hundreds.

According to the NRA’s official website, the three-day Indy convention was offering up ’15 acres of guns and gear, exclusive seminars and luncheons, appearances from top national political leaders and musical superstars, and the chance to rub shoulders with tens of thousands of other Second Amendment patriots’. Photo: Getty

That didn’t seem to bother the NRA members at the convention who insisted the group remains as influential as ever.

“Why do you think Trump and Pence are coming here?” asked Roger Frasz, a lifetime NRA member and gun shop owner in Prescott, Michigan, who was wearing a red “Trump 2020” hat.

Exactly how much influence the group will wield though in 2020 remains unclear.

The NRA, its policy arm and its political committee did not respond to requests for comment this week.

But Andrew Arulanandam, the NRA’s managing director of public affairs, has said recent reports of turmoil and financial troubles have been exaggerated and are fuelled by anti-gun forces.

However, Evergreen took to Twitter to reveal growing tensions between NRA president Oliver North and it’s CEO Wayne LaPierre, describing the organisation as dysfunctional.

BREAKING: NRA President Oliver North is reportedly pressuring CEO & Executive VP Wayne LaPierre to resign.

The evidence of the NRA’s mismanagement and dysfunction is mounting by the day. Meanwhile, the gun safety movement just keeps growing. https://t.co/gXLwunAyQr

— Everytown (@Everytown) April 26, 2019

Mr Trump, too, was dismissive of suggestions the group’s power was waning, tweeting that the “(at)NRA is getting stronger & stronger” before he left Washington.

“Having their powerful support has been vital to (hash)MAGA!” he said.

Still, the NRA is having financial issues, according to an analysis of tax filings by The Associated Press. The tax-exempt organisation’s 2016 and 2017 filings, the most recent years available, show combined losses of nearly $US64 million ($90 million).

Income from membership dues plunged about $US35 million ($49 million) in 2017. And revenue from contributions, grants and gifts dropped about $US35 million ($49 million).

But even if the group cuts back from the record $US412 million ($585 million) the NRA’s nonprofit wings spent during the 2016 election year (that’s in addition to the $US30 million ($42 million) two NRA political action committees invested in electing Mr Trump), the group is expected to be an active spender in the election.

-AAP