WASHINGTON: Donald Trump has discovered that in America there is one issue that even he cannot fool with. The bloviating billionaire asserted on Wednesday that in a Trump presidency there would be "punishment" for women who choose to have abortions.
It was a classic move by a Republican presidential candidate for whom espousing extreme solutions to key policy issues has become a trademark: America should kill the families of jihadists (foreign policy); it should torture its prisoners (national security); ban Muslims from entering the country, and build a wall on its southern border (immigration). And as his frontrunner status shows, his tactics have helped.
Not so with abortion. Barely had the words left his mouth before Mr Trump faced a firestorm of criticism from all sides of the American political debate. Democrats, Republicans, pro-choice and pro-life groups alike launched attacks so fierce that, like a wounded animal, Mr Trump was forced to retreat.
He should have known better than to meddle with this topic. More than national security, more than healthcare, more even that guns, abortion is the issue in America that can bring neighbours to blows.
It's a ferocious battleground that has once again reached the Supreme Court, with a Texas case now being heard which has the power, potentially, to render obsolete the breakthrough 1973 Roe v Wade decision that struck down abortion bans.
Many states are already doing their utmost to bypass that landmark ruling, putting up legal barriers that hamper an abortion clinic's ability to operate and a woman's access to it.
But why is this topic so uniquely febrile in the United States?
Religion, you say. This is a Godly country yes, but it's one in which the religious Right is actually losing strength. Last year, remember, America became a liberal standard bearer on gay marriage, legalising same-sex unions. And all the statistics point to a singular fact: America is becoming more secular. Even the fundamentalist Christian bloc is shrinking, with 22 per cent of white evangelicals born in the Eighties now saying they have no religion, almost double the number of the decade before.
The real answer is that in an increasingly partisan country, abortion is uniquely, and perfectly, divisive. Abortion, opinion polls show, splits America, and has always split America, into two equal halves. So while political parties can win the argument for a time, they can never settle it forever.
It's no surprise, then, that a recent poll found that, for a record number of Americans, a politician's stance on abortion is the single most important factor in shaping how they vote. Mr Trump should have known better than to mouth off.
His reaction to the fallout was telling: humility, apology, backtrack - the kind of compromises that the career politicians he so derides make all the time.
As we move towards the sharp end of this presidential campaign, it shows how he will behave when his usual bluster doesn't work. He will behave like everyone else.
This may be the first political U-turn for The Donald, but if he goes much further, it will certainly not be his last. And it shows why he may not be as iconoclastic - or invincible - as his passionate supporters believe.