It was sometime in the late 1990s that I first interviewed Alan Webster about New Zealand’s part in a global Values Study. It’s a fascinating snapshot of values in countries all over the world and I still remember seeing America grouped with many developing countries on a spectrum that had most English-speaking, democratic and developed countries grouped at the other end. It charted belief in angels and other supernatural beings. It was a lightbulb moment that has always helped me remember how deep religious beliefs run in the US and how socially different it is from most Western, Enlightenment-inspired countries.

That memory came back to me this morning when I awoke to the news the US Supreme Court has overturned Roe v Wade in a 6-3 ruling, eliminating a woman’s constitutional right to an abortion; a right that has been in place since 1973. Abortion rights will now be decided state by state, with 26 states ready to enact laws that ban abortion, often with no exceptions. That means no abortion even in cases of rape or incest.

It is undoubtedly a landmark moment in US politics and law, the latest step (not the end) in a decades-long campaign by conservative Americans to overturn America’s most controversial and divisive law. Writing the majority opinion, Justice Samuel Alito wrote that “far from bringing about a national settlement of the abortion issue Roe and Casey have enflamed debate and deepened division.”.

He’s right, but the implication that this ruling somehow calms the waters is either deeply naive or deeply cynical. It does nothing more than flip the issue, like the handover of the ball in a football game, with what has been the team on defence now going on attack and vice versa. And because change in and of itself is fuel for any fire, this only ensures abortion remains THE divisive issue in American politics for, well, who knows how many years to come.

Abortion has divided the country for decades; more so than foreign wars, economic policy and even gun control. It is the answer to so many questions non-Americans have about US politics.

Many around the world have been perplexed by the growing divisions in US politics, the loss of civility, the rise of Trump. There are answers there about the influence of money, taxes, changing demographics and more. But at the heart of US political polarisation, often unspoken, masked or downplayed, has always been abortion.

One of the most confounding of political mysteries in the past decade was why 84% of white evangelicals in 2016 voted for a thrice-married alleged sexual abuser as president and why “character” suddenly fell down their list of voting priorities. Today’s court decision is the answer. Evangelicals are motivated by abortion more than any other issue and Trump’s commitment to swaying the court against it convinced them to vote for him even when it was against their economic interests and compromised other values.

Many in conservative religious circles in the US compared Trump to King David, arguing that God has long used flawed and corrupt individuals to bring about his will. That faith has been vindicated today and Trump’s status as a moral hero is enshrined, despite his many other sins.

Such is the strength of belief for or against abortion. Its power to divide is so strong because, seen through different lenses, it is so obviously right or wrong to those on either side of the debate. It is, to those on either side, obvious that they are right and they are horrified - not just perplexed, but horrified - that anyone might disagree with them. Those celebrating today’s overturn are celebrating the end of mass murder, because to them the decision to abort a foetus is the decision to take a life. (Others, to be fair, see it as a legal issue, one that is not in the constitution and so should always have been viewed as a political debate not a constitutional right). Those weeping over today’s ruling do not see a foetus as a human life and rather see the courts telling a woman what she can do with her body, right to the point of that woman’s life and death.

When both sides see their view as a matter of life over death, you can understand the depth of feeling and pain on both sides and that, whatever Alito may be hoping, that today’s decision will do nothing to deal America.

What’s more, the impact of today’s ruling on US politics will be deep. Three things stand out.

• Reproductive rights will dominate the 2022 mid-term elections and the US presidential elections in 2024. The court has said abortion is not a constitutional right, therefore it is up fr grabs politically. Debate over national bans v national rights has already begun. That will mean less political oxygen for pressing political issues such as climate change, China and the Ukraine invasion.

• This could be the start of a conservative pendulum swing in US politics, led by the US Supreme Court. Judge Clarence Thomas in his support of the majority opinion suggests the now reliably conservative court could dive further into America’s moral dilemmas, ruling on same-sex marriage and contraception rights.

• Perhaps most troubling, it undermines citizen’s faith in their major public institutions. A majority of Americans favour at least some rights to abortion and some gun control. This week the Supreme Court has issued rulings at odds with public opinion on both. At a time when core institutions such as Congress and the media are losing the trust of citizens, adding the courts to that list is a major worry. If the foundations of liberal democracy are not serving the people, then those people start to look for alternatives, the baby can be lost with the bathwater and whole systems of law, order and government can start to look fragile.

These are perilous days for the American project and that has implications for all of us. Today’s court ruling is yet another polarising decision in these most polarising times and it’s hard to see where the healing can begin.