Donald Trump, the presumptive Republican presidential nominee, promises supporters in Texas that he would protect their right to bear arms.

Australia's former deputy prime minister, Tim Fischer, has proposed what is surely a world-first plan for shooting down the gun-loving US Republican candidate for president, Donald Trump: a "massacre tax" on US gun exports.

In doing so, Fischer has also come out all guns blazing against what he calls the "lethal poison" flowing to Australia from US weapons manufacturers with the assistance of the American gun lobby and what he calls dysfunctional and corrupted US policies.

Fischer's suggestion?

ALEX ELLINGHAUSEN/FAIRFAX AUSTRALIA Tim Fischer says 'lethal poison' flows to Australia from US weapons manufacturers.

If Trump becomes president and makes good on his threat to welch on free trade agreements and to take America out of the World Trade Organisation, the international community should slap a massive tariff on all guns and ammunition produced and exported from the US.

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REUTERS Democratic and Republican US senators make arguments on four different gun control measures that were all voted down in the aftermath of a massacre that left 49 people killed in Orlando.

Such a tariff should be calculated on a scale equal to the number of gun massacres in the US in the previous year, Fischer suggests.

On current figuring, that would equate to a tariff of 372 per cent this year.

Delivering the Frank Larkins Oration at Melbourne University's International House on Thursday evening, Fischer - who is Australia's former trade minister - pointed out that all US-produced guns and ammunition that were imported legally into Australia had benefited from a zero-tariff rating for some years.

"So the lethal poison flowing from the dysfunctional gun policies of the USA is facilitated over US borders to this part of the world," he said.

"Now last year - 2015 - there were 372 'gun massacres' in the USA.

"This year Donald Trump has threatened to take the USA out of the WTO.

"Let me leave you with the thought that if he does, all OECD countries should immediately impose a tariff or 'Levy Assisting Gun Safety' or LAGS, equal to the number of gun massacres in the USA for the previous year.

"So impose a tariff at 372 per cent."

The FBI defines mass murder as the murder of four or more persons during a single event. The US' Congressional Research Service defines a "public mass shooting" as one in which four or more people selected indiscriminately, not including the perpetrator, are killed. On these definitions, a mass murder occurs, on average, almost every day in the US.

Fischer conceded his was an unusual proposal "that will infuriate the NRA and the USA".

"But at present you are 15 times more likely to be shot dead in the USA than Australia per capita," he said, adding that an estimated three-quarters of gun crime in Mexico is committed with weapons flowing over the border from the US.

"The gun poison and policy dysfunctionality of the USA is now so bad, our human rights, miles from the USA, are impacted."

Fischer was National Party leader and deputy prime minister when he and prime minister John Howard pushed through Australia's gun laws in the wake of the Port Arthur massacre in 1996.

Fischer said that immediately after the Orlando massacre, where 49 people were shot dead in a nightclub on a single night, the US Senate had voted down approving weapons background checks on those on the "no-fly" list.

This demonstrated "sheer corruption of public policy settings" in the US, and proved that something was very rotten within the US power structure, Fischer said.

Voicing concern that "the shouting of Donald Trump types, the Bernie Sanders sway on the Democrats and Hilary Clinton", and protectionist pressures from the post-Brexit saga were endangering international trade, Fischer said it was "time to rebrand the world trade equation if we are to win back the debate against those who contend all trade is a net negative and the root cause for all the economic ills in the world.

"Elements of major political parties in the USA and other countries are today solidly against trade and so-called free trade," Fischer said.

"As we do battle in the public square, let us delete the term 'free trade' and insert a more accurate term: 'facilitated trade'."