Those of us too young to remember the Vietnam War have long wondered why such a pointless endeavour dragged on for so long. Thankfully, we have America's unrivalled appetite for introspection to satisfy our curiosity.
In slow intimate detail, it lays out the US experience of the 1960s and 1970s through the prism of the ever-growing conflict in South-East Asia.
It is clear on a point in the weeks before the assassination of president John F Kennedy in 1963, when Washington could have halted the failing venture. Thereafter, an unholy alliance of dissembling politicians, officials and military men perpetuated conflict.
It dragged on and Americans revolted against their failing leadership.
First known as counter-culture, the insurrection eventually became a social revolution, transforming attitudes to individual rights and institutions, such as marriage.
A baby boomer president, Donald Trump is a product of the 1960s. Those cultural wars are now shaping his presidency.
Watching the US leader in real time as he ignited the headlining-grabbing feud with the National Football League last week, it was clear that this ground is where he feels greatest comfort.
The US president was in Alabama speaking on behalf of a flailing centrist candidate for the senate. The candidate was beaten a few days later by a far right former judge who had been barred from office for allowing religion, not the law, to underpin his verdicts.
American newspapers reported a defeat for Mr Trump but a victory for Trumpism.
During the speech, it was apparent Mr Trump sensed he was on a losing proposition. He suggested at one point that he had "maybe" made a mistake being there.
He reached to find a missing connection with the audience, lashing at the National Football League players “taking the knee” during the national anthem. Wouldn’t it be good if the owners fired the (mostly black) protesting players on the spot, he asked, drawing cheers from the crowd.
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The remarks triggered a wall of outrage from above and below within the NFL. Patrician owners lined up to keep faith with their stars. The players bonded to make the kneeling during the anthem a point of unity.
Mr Trump is not fazed by the row, celebrating his intuitive instinct to reach his own supporters.
The more technical rows of the Trump presidency often hog the headlines. Can the Republicans pass an alternative to Obamacare? Will the biggest tax reform package in a generation succeed? Can the US renegotiate Nafta and other trading relationships as it seeks fair trade not free trade?
The NFL conflagration demonstrates that it is the gut-driven demands from the presidential bully pulpit that will ultimately define the Trump legacy.
The divisions of the Vietnam War split open US society. Trump voters have largely borne a greater toll of death and loss since the conflict, both on the battlefield and homefront. Well-paid manual labour jobs disappeared. Social reforms have not compensated for their setbacks. Family structures disintegrated. Just 26 per cent of working class adults were married last year, less than half the number just 25 years ago.
A curious paradox is those most attached to conventional ideas are least likely to attain these in practice. Americans with a bachelor’s degree, who have benefited from the liberal society forged since the 1960s, are meanwhile positively conformist. The same study says 56 per cent of upper class adults are married.
The election of Donald Trump was a rallying cry for a restoration. Not to bring the country back to where it was before Vietnam. It was instead a roll of the dice for new equilibrium where being poor does not put people at a distance from their ideals.
To make it work Mr Trump has to hold the line and channel his voters into a movement. Ramping up of divisions is a means to an end.
That is the pertinent question. What is the end?
A partial answer is that too many Americans feel things are not going their way. After Mr Trump's speech to the United Nations, one Manhattanite observed the only thing he liked about the president was that no one would mess with America with him in charge.
Attitudes can change. Trends in international trade favour reshoring of US production. The tech giants are desperate to bring back hundreds of billions stashed overseas to invest in America. After ending Barack Obama's strategic patience, this is right time to confront North Korea. A border wall could forestall an immigration crisis with Latin America. But racial friction is unlikely to resolve as long as there are police shootings and clashes over Confederate statues. Health care is the Gordian knot of both politics and the economy.
When will America feel it is set on the right direction? Not until a new political generation has taken over from the trenchant Mr Trump.