The most important political news stories occur when the strivings of politicians are caught up with a powerful groundswell of public emotion.
When issues of great moment "cut through" to ordinary people, nobody quite knows how it is all going to turn out.
Such political events crop up perhaps only once a decade. Most recently Britain has experienced fierce domestic turmoil around the 2016 Brexit referendum and the US/UK invasion of Iraq.
The rights and wrongs of the miners' strike defined the 1980s. These were all issues on which the destiny of nations depended. The tragic death of a famous young woman would not seem to fit into this category, but it does.
The death of Princess Diana, 25 years ago, in a car crash in Paris in the small hours of 31 August 1997 sparked an overwhelming wave of grief and soul searching that shook the pillars of Britain's unwritten constitution with reverberations that are still felt today.
In death, Diana has become even more iconic than when she was one of the most famous and controversial women in the world. No significant anniversary passes without a cluster of new films. The Princess is currently on Sky Documentaries. Channel 4 is running a four-part series Investigating Diana: Death In Paris.
In November, Elizabeth Debicki will take over the role of Diana in series five of The Crown, when the reality drama will presumably cover her death. She has been portrayed on screen by A-listers including Naomi Watts and Kristen Stewart. Diana The Musical has already been on Broadway and made into a film.
Twenty-five years ago, Diana was more than a starring role. She was the subject of universal interest and near universal sympathy - as the mother of two young boys and the cast-off wife of Prince Charles, the heir to the British throne.
Like the assassination of President Kennedy in 1963, people remember when they heard the news. Many Britons, including me, were drowsily preparing to go back to work after the August break.
When the Sky newsdesk woke me around 5am with the news that Diana and Dodi Al-Fayed, her boyfriend, were both dead, my first question was "What - suicide pact?"
It was an overreaction but reflected the melodramatic circumstances in which Diana found herself at that time.
She had cultivated the impression that she was a victim at bay, not least in the unprecedented revelations she made about her private life, first to the journalist Andrew Morton for his book Diana: Her True Story and then in a BBC Panorama interview with the reporter Martin Bashir.
Although Diana routinely demanded privacy, her response to the breakdown of her marriage was to build up her status as an international celebrity. She attended the funeral of the fashion designer Gianni Versace alongside Elton John and was not shy about the new men she dated.
By the summer of 1997 there was a growing sense that her life in the fast lane was close to spinning out of control, even before Paris. The lives of previous most photographed women in the world, such as Marilyn Monroe, had ended badly.
Bernie Taupin would rewrite the lyrics of Goodbye Norma Jean into Goodbye England's Rose for Diana's funeral in Westminster Abbey.
In the meantime, the pictures of Diana's holiday with Dodi in St Tropez and on board the yacht of his father Mohammed Al-Fayed, the controversial owner of Harrods, were all the paparazzi and gossip columnists could have wished for.
Diana was also beautiful, charming and empathetic. Her charity work, notably concerning AIDS and land mines, was ground-breaking and had an impact which endures to this day.
She was a loving, model, mother to her two boys, William and Harry, both in the line of succession for the Crown. She was vastly more popular with the public than Prince Charles, although, unlike him, she no longer had a constitutional function.
The mass outpouring of grief at her death came as a shock. Crowds jostled outside Kensington and Buckingham Palaces at all hours to lay flowers, often laced with intimate personal messages. To the controversialist Christopher Hitchens it was "an orgy of sentimentality" but it was impossible to cover anything else, certainly on Sky News.
The internet existed then but there was no social media. The news unfolded live on television, as Prince Charles flew to Paris that Sunday to oversee the return home of her coffin.
As depicted in The Queen, the first of The Crown author Peter Morgan's royal dramas, the Queen was in Scotland with her grandsons and they did not return to London for some days. Reflecting the public mood, tabloid newspapers turned on the Royal Family - demanding to know why there was no flag flying at half-mast above Buckingham Palace.
In contrast to the royals, the recently elected Labour government acted swiftly. Tony Blair epitomised Diana hours after the news broke with the phrase "she was the people's princess". It was the only time I can recall when the future of the monarchy and whether Prince Charles should become king were discussed openly and freely in the mainstream media.
Downing Street worked closely with the palace on the funeral and other arrangements, subsequently leading to resentment towards the Labour government by some courtiers. William and Harry still harbour great bitterness towards the media as well.
The Queen returned to the capital and made a rare and moving live broadcast, with the mourning crowds visible behind her on the Mall. She walked out to meet some of those laying flowers.
I was based at Canada Gate covering the funeral and there was a chilly silence punctuated by the occasional boo when the Queen led her household out on foot to salute Diana's passing cortège.
Mohammed Al-Fayed maintained that Diana and his son had been murdered by agents of the British State. It was not until 2008 that an inquest, aided by an inquiry headed by former Metropolitan Police Commissioner Lord Stevens, concluded they had been unlawfully killed by the "grossly negligent driving of the following vehicles [the paparazzi] and of the Mercedes driver Henri Paul".
In the absence of a rival centre of attention in subsequent decades, the monarchy has consolidated the position of the direct line to the throne - Elizabeth, Charles, William, George - through golden, diamond and platinum jubilees.
Once vilified, Charles' wife and long-time mistress, Camilla, Duchess of Cornwall, is now a popular member of the firm, who Her Majesty has decreed will become his Queen.
The sad story of Diana will never be forgotten. It may yet have profound consequences for Prince Charles and his heirs.