President Donald Trump has made clear his support for the gun lobby and, paradoxically, an increase in "active-shooter" incidents has led to a decline in public support for stricter gun laws. (The US Department of Homeland Security defines an active shooter as "an individual actively engaged in killing or attempting to kill people in a confined and populated area; in most cases, active shooters use firearms and there is no pattern or method to their selection of victims"). Many Americans believe that, if more citizens were armed, deranged gunmen would be eliminated sooner.

The best recent chance for stricter US gun laws was under the Obama administration in 2012 after the horrific massacre of 20 primary school students at Sandy Hook Elementary School. Despite his best efforts, president Barack Obama found he was unable to change federal gun laws because too many federal politicians relied on support from the powerful National Rifle Association, or were unprepared to suffer an NRA and gun-lobby-orchestrated backlash at the next election.

The NRA is now more powerful than ever. It contributed $US30 million to Trump's presidential campaign fund. Trump was the first sitting President to address an NRA conference.

For 10 years from 1994, US federal law did ban the sale of many types of assault rifles as well as high-capacity ammunition magazines. But the law expired after a decade and, in 2004, there was little political will to renew it.

The best chance for tighter US controls lies at the state level. From 2004, some states continued to restrict the types of weapons that can be bought. Nonetheless, some of the laxest gun controls are in "frontier states" like Nevada, where the latest shooting took place.

Theoretically, at least, there could be nationwide uniform restrictions on firearms ownership without breaching the US constitutional "right to bear arms" – for example, limits on which types and how many weapons could be held by individual Americans. (Convicted felons and people with mental-health issues are already excluded from owning some guns, but these exclusions are not effectively enforced.)

The second amendment of the US constitution reads: "A well-regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed." But its proponents never anticipated giving every American the right to acquire an armoury of high-powered weapons – as Stephen Paddock and many other active shooters before him did.

I visit gun shows in the US fairly regularly to see what is potentially available for security reasons. In July, for example, on offer were long-range sniper rifles, semi-automatic weapons (adjustable to fire on automatic) and M79 grenade launchers. All you needed to buy them was a driver's licence. Gun-show vendors are usually not fussy about where the licence is from – and will happily accept a non-American licence.

Meanwhile, American fireworks shops sell mortar-type fireworks and rockets with explosive heads that could easily be adapted to kill. Powerful drones are available over the counter that could be used to drop explosives on mass gatherings. In fact, given the range of options in the US for killing people, it is surprising there are not more mass-casualty incidents.

As well as the weapons that are designed to be automatic, some weapons that are not automatic can easily be made automatic. When I was in the Australian Army, the standard issue rifle was the 7.62mm self-loading rifle, or SLR. A matchstick in the right place turned the SLR into an automatic weapon. In South Vietnam, many of our soldiers did just that with their SLRs. Most military assault weapons now have a single-shot/semi-automatic/automatic capability because it makes them more versatile and effective in combat.

Australia's gun buy-back program in 1996 and adoption of strict gun-control laws were a consequence of Martin Bryant's active-shooter attack that killed 35 people at Port Arthur in Tasmania. Our buy-back program led to the destruction of 660,959 weapons. However, the total number of firearms in Australia has been creeping back up, despite another buy-back in 2003 and an amnesty this year.

While the scale of our security problem is nowhere near that of the US (or France), we have no reason to be complacent given the ongoing threat of violence by right-wing extremists, Islamist extremists and people with mental illnesses. Australian police forces need to continue to have the resources and training to be able to respond quickly and effectively to active-shooter attacks.

Clive Williams is an honorary professor at the Australian National University's Centre for military and security law and an adjunct professor at the Australian Defence Force Academy.