To boost Donald Trump’s prospects of becoming president, the National Rifle Association is poised to pour more than $15m into ads in several battleground states to defeat Hillary Clinton, the most vocal pro-gun-control presidential candidate in years, according to an NRA board member.

The NRA has already plowed almost $6.5m into TV spots in several key states bashing Clinton and one NRA board member told the Guardian that the pro-gun goliath will spend “multiples” of that figure by election day on the presidential contest.

Next week, the NRA is slated to launch another seven-figure round of TV ads in Nevada, North Carolina, Ohio and Pennsylvania. Last month, the NRA made a $3m ad buy in these states that branded Clinton as a “hypocrite” for accepting secret service protection, while calling for more gun control, which the ad charged “would leave you defenseless”. An earlier NRA ad buy attacked Clinton on Benghazi.

In 2012, the NRA spent $15m in the hope of making Barack Obama a one-term president, and this year’s spending to defeat Clinton is expected to surpass that sum, according to the board member and another NRA source.

The five million-member NRA’s embrace of Trump, who once backed more gun control measures, has been spurred in part by its intense fear of a Clinton presidency.

Democrats running for president have traditionally shown “trepidation” about calling for more gun control, notes Matt Schlapp, the chairman of the American Conservative Union. But this year, Schlapp told the Guardian, “the NRA and gun enthusiasts are faced with the specter of a Democrat running for the White House embracing additional gun control”.

The NRA disdains Clinton’s advocacy of moderate gun control measures –including expanding background checks on gun purchases and reinstating a ban on assault weapons to curb mass shootings – but is fearful that she would nominate supreme court justices who do not concur with the NRA’s staunch opposition to new gun controls.

“This race is probably more about the supreme court than anything else from the NRA’s perspective,” said the NRA board member.

The supreme court stakes are high: the vacancy created by the death of conservative Antonin Scalia is likely to remain open until the next president takes office. And the NRA is especially concerned that a more liberal court might overturn an earlier supreme court decision, known as Heller, which established an individual’s right to keep a handgun in the house for self-defense.

Significantly, the NRA’s endorsement of Trump in May at its annual convention came earlier than usual: Mitt Romney and John McCain had to wait until October in 2012 and 2008 to get the NRA’s blessing.

The NRA’s commitment to Trump was underscored when Chris Cox, the NRA’s top lobbyist gave a primetime speech at the GOP convention this summer, a first for the increasingly GOP-oriented pro-gun lobbying behemoth. A senior GOP operative noted that historically the NRA “tries to stay assiduously non-partisan. The dynamics of speaking at a convention are a little dicey.”

The NRA’s big campaign blitz has been partly fueled by an aggressive fundraising operation which in recent years has targeted mega-donors. In 2014, for instance, the NRA received $4.9m from Freedom Partners Chamber of Commerce, the financial hub of the conservative advocacy network backed by the billionaire Koch brothers. The NRA is hoping to pull in another seven-figure grant this year, say two NRA sources, although nothing has come in yet and the Koch network itself is not focusing on the presidential race and Trump has been sharply criticized by Charles Koch.

The NRA’s entree to the Koch world stems in part from bonds that the gun group’s top officials have forged. One donor who goes to the twice-a-year policy and fundraising retreats hosted by the Koch network, told the Guardian that the NRA’s top executive, Wayne LaPierre, has attended them on a couple of occasions, affording him a chance to pitch and schmooze with big network donors such as investor Foster Friess.

Another key big-money link involves the hedge fund tycoon Robert Mercer, who has given a pro-Trump Super Pac at least $2m, and is also a lifetime NRA member and a Koch network donor. This year Cambridge Analytica, a voter data firm in which Mercer is a key investor, has worked with the Herald Group, a DC-based consulting firm, to implement the NRA’s “Trigger the Vote” drive to register new voters and get them to the polls. i360, a big voter data firm that is closely tied to the Koch donor network, has also been involved in the Trigger the Vote campaign.

The pro-Trump blitz comes despite the real estate mogul’s earlier backing for a ban on assault weapons and longer waiting periods for background checks with gun purchases, ideas that the NRA has rejected. But Trump’s high-decibel anti-gun-control rhetoric this year seems to have ingratiated him with the NRA brass, and coupled with the strong pro-gun records of Trump’s two sons, proved instrumental in winning the NRA’s backing.

Trump and the NRA parted ways briefly earlier this year, when Trump responded to the Orlando massacre by suggesting that if the nightclub where it took place had allowed its guests to bring in arms, then the killings could have been averted. The NRA quickly shot back to distance itself from Trump: speaking to an ABC news show, the group’s top lobbyist, Cox, said that Trump’s calls for arming people in clubs “defies common sense. It also defies the law.”