The terrible irony is that an Australian terrorist should commit such an atrocity in New Zealand when the Australian government has been deporting hundreds of New Zealand citizens because of criminal records in Australia. To my knowledge there is no evidence of any serious crimes being committed subsequently by any of these individuals.

The second terrible irony is that such an horrific crime should be committed against Muslims given the greater concentration by the Australian government and society on the dangers of Islamist terrorism. Since the Bali bombings there have been Islamist attacks on Australian soil but nothing to match the mass carnage wrought in Christchurch.

The term "shock wave" is often used loosely, but on this occasion the shock has reverberated across both countries. As scarcely an institution has been left untouched, it is hard to know where to start.

New Zealand Prime Minister Jacinda Ardern occupied centre-stage as the main public official responsible for speaking to her own citizens and directly to the world. She was remarkably clear-headed and steady in calling out the terrorism as an attack on "us" by someone who had demonstrated by their actions that they were not representative of "us".

Her language bound New Zealanders together at a time of great pain and suffering and she did this without flowery language or unnecessary rhetorical flourishes. She came through this test most impressively as a person with a big heart and a clear mind. She did not over-promise guarantees of safety in response to such a tragedy. The massacre had already proved that safety cannot be guaranteed and any such promises by political or police authorities are hollow.

She immediately addressed the question "how could this happen?" by calling on her intelligence services to explain how such an individual could not be on a terrorism watch list and promised gun law reforms to limit the possibility that anyone in the future could accumulate automatic weapons as this terrorist had done.

Intelligence services in both our countries will have to consider whether they unwisely downplayed white racist, anti-Muslim terrorism because they were carried along by the prevailing concentration on Muslims as terrorists.

The awful fact that the killings were filmed by the perpetrator and distributed in real time via social media is so shocking that once more there are calls for restrictions, without great anticipation that the social media colossus can ever be tamed.

Such tragedies do bring communities together and overcome social and political divisions at least temporarily. Religious leaders and political figures made extensive and heart-felt gestures of solidarity. The Muslim community has been most gracious given the massacre they have suffered.

Soul-searching in the wider community has been so deep that the famous Christchurch rugby football team, the Canterbury Crusaders, has even reflected whether its name should be changed because of the anti-Muslim connotations of the term "crusaders", which originated in the anti-Muslim Christian religious crusades of the medieval period.

Not surprisingly the standard pro-Western crusades story taught in schools is contested by Muslims. No matter how much that history is forgotten in modern society, in which the term crusading has lost its original religious connotation, such a gesture of reconciliation would be a remarkable symbolic outcome akin to some of the name changes in modern post-apartheid South Africa.

Political divisions soon arose however at the extremes and in the mainstream, though bipartisanship has been maintained among the major parties at the federal level.

The Independent Queensland Senator Fraser Anning made anti-immigration and anti-Muslim remarks entirely in character with his previous extremist parliamentary outbursts. He was unrepentant in the face of bipartisan censure by the Prime Minister and the Leader of the Opposition and widespread community outrage.

The new Muslim Greens Senator from NSW Mehreen Faruqi, the first-ever female Muslim senator, developed her recent anti-racism maiden speech into a powerful wider criticism of the way right-wing views are encouraged in the general community by leading politicians who are tolerant of them and backbenchers who encourage them. The Greens were then unreasonably compared to Anning by Peter Dutton, when the reasonable equivalent for the Greens is the Nationals.

The more serious divisions came in the context of the New South Wales election campaign where gun-control was already a political issue. The hook has been the electoral threat posed by the Shooters Fishers and Farmers party to the government in several rural seats and the preference exchange between Labor and the SFF in two of those seats.

The Christchurch massacre has magnified these twin factors. The state Coalition government has brought out former prime minister John Howard, known for his anti-gun record following the Port Arthur massacre, to campaign against the SFF and by implication Labor.

Labor’s preference exchange was always problematic and the question is whether SFF preference deals should be beyond the pale as One Nation deals once were. Where on the continuum between extremist and legitimate is the SFF party? Is gun control campaigning ethical or opportunistic in the context of human tragedy? The answer to these questions will come unfortunately in the hot-house last week of a desperately fought campaign. Whatever the answers the electoral impact is hard to measure, which also applies to the possible impact on the federal election campaign.

The larger question about shock waves, like the one Australia and New Zealand is currently experiencing, is whether the consequences are permanent or merely temporary. Societies can quickly forget the lessons if business as usual returns despite the horror.

John Warhurst is an Emeritus Professor of Political Science at the Australian National University.