The Port Arthur massacre not only overhauled our country's gun laws, it fundamentally changed Australia.

The horrific event is carved into the country's psyche as the moment where Australians collectively stood up and declared that this horror should never again happen in our country. It has become a line-in-the-sand issue — violating the Port Arthur gun law compact is politically risky.

It is in this context that the Prime Minister has announced the Liberals will preference One Nation below the Labor Party at the federal election.

Political ammunition

It was only after the Al Jazeera investigation revealed One Nation leader Pauline Hanson appearing to suggest the Port Arthur massacre was part of a conspiracy that Scott Morrison had what he saw as the adequate political ammunition to declare that the Liberal Party will put One Nation below the Labor Party on its how-to-vote cards at the upcoming federal election.

It took the memory of the horror of Port Arthur for the Prime Minister to be able to strong-arm his own party — crucially the Queensland branch — into what is a symbolic and principled position on preferences to the One Nation party.

Several MPs in the Liberal Party tell me they are disappointed it has taken so long for this declaration, that the optics of the Liberal party being seen to prefer One Nation to the Labor party or even the Greens is "toxic" in states like Victoria and in safe Liberal heartland seats where the party is battling for survival.

But instead of pointing the blame at Mr Morrison, several blame the Queensland branch of the LNP who they say had to be dragged kicking and screaming to this position.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 1 m PM says Liberals will preference One Nation below Labor.

The Howard legacy looms large

One MP tells me it had to reach an "untenable" situation before the Prime Minister could secure an assurance from Queensland that they wouldn't just undermine him on such a call. The memory of Port Arthur was that untenable turning point.

Another MP says Mr Morrison may have delayed over the past few weeks on this issue, but he deserves credit for moving more quickly than John Howard, who ultimately declared One Nation would be put last in 1996.

Scott Morrison has also revealed he had discussed preferences for One Nation with Mr Howard, who overhauled Australia's gun laws following the 1996 Port Arthur massacre.

The Howard legacy looms large over the Coalition's current political dramas.

The Prime Minister's commitment comes after several weeks of sustained and relentless pressure to make this declaration in the wake of the Christchurch attack and the subsequent conversation about the mainstreaming of white supremacy in the political debate.

Australia's strict gun laws are a line-in-the-sand issue and pushing to change them is politically risky. ( Reuters: David Gray )

Why did the decision take so long?

Press conference after press conference, Mr Morrison had held firm, refusing to commit to putting One Nation last or even below Labor on Liberal how-to-vote cards.

The horror of the Christchurch attack — where 50 Muslims were murdered while praying by an Australian white supremist — changed the discourse around One Nation and Fraser Anning.

No longer were moderate Liberals prepared to stay silent — and one by one, they began publicly declaring their view that One Nation should be put last or behind Labor and the Greens.

From leading moderate minister Simon Birmingham, to Kelly O'Dwyer, Tim Wilson, Trent Zimmerman, and even former deputy Liberal leader Julie Bishop. All of them went on the public record to declare that One Nation should be down the bottom of how to vote cards. But still this issue did not lead to a change in position.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 8 seconds 1 m 8 s One Nation's Pauline Hanson and James Ashby on a hidden camera

Game changer: Pauline Hanson

In the end, the game changer was Pauline Hanson's absurd and offensive claims about the Port Arthur massacre.

The Prime Minister said his decision was "based on our strong view about the sanctity of Australia's gun laws and to ensure that at no stage that those things should ever be put at risk" and there would be no "trading on the issue of those gun laws".

Podcast The Party Room One Nation faces fallout The PM says the Liberals will preference One Nation below the Labor Party at the upcoming federal election. What could it mean for the final result? About

About Subscribe

Subscribe RSS Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen More great ABC podcasts

It is worth noting the things Ms Hanson has said that were not considered alarming enough for the Liberal Party to change their preferences. Ms Hanson has compared Islam to a disease Australians need to vaccinate themselves against. She has called for a ban on Islamic immigration. These comments did not force the Liberal Party's hand, but some moderates believe that they should have.

So now, how does Pauline Hanson respond?

MPs who are fighting for survival in Queensland are sweating on her retaliation.

NSW One Nation MP Mark Latham, the former federal Labor leader who was elected to the State Parliament Upper House at the weekend, warned retaliation action from his party would cost the Liberals seats at the May federal election.

He listed the NSW federal seats of Banks, Gilmore, Hughes, Robertson, Riverina and Parks as having benefitted from One Nation preferences in the past.

Several Liberal MPs fear that this decision may lead to electoral death for them. They fear that Labor will be the ultimate beneficiary of this latest preference decision.

Patricia Karvelas is the presenter of RN Drive.