You can argue about when the contemporary era of white male reaction in American politics began. But surely March 8, 1970, four days after National Guardsmen opened fire on students at Kent State University, deserves a hearing.

On that day, a student protest in Manhattan against the shootings in Ohio was met by a counteroffensive — the “Hard Hat Riot”. Dozens of construction workers organised, marched and clobbered the protesters, kicking them and beating them with hard hats in what The New York Times described as a “wild noontime mêlée.”

The construction workers were sick of hippies, sick of leftists, sick of privileged college children complaining about the war and the draft and the country. Some rioters branched off to Pace University, near City Hall, where they beat up more children after having been pelted with objects hurled from the school’s roof. Less than three weeks later, president Richard Nixon welcomed a delegation of hard hats to the White House. The riot was extreme. But the combustible mix of resentments and prerogatives that it channelled has resurfaced time and again for half a century. In the spring of 1995, months after a midterm election in which “angry white males” were credited with powering Republicans to an historic victory in Congress, president Bill Clinton said that it was a psychologically difficult moment “for a lot of white males — the so-called angry white male”.

The angry white males who vexed Clinton in the 1990s were muted during the presidency of George W. Bush. But for some, the psychological adjustment to empowered women and a more diverse citizenry never did arrive. Under Bush’s Democratic successor, the angry white guys promptly reappeared, recast as the Tea Party, to wage a culture war under the guise of a tax protest. The flowering of Donald Trump’s campaign this summer arguably represents the political peak of the angry white male. In Trump, the aggravated and aggrieved have a presidential candidate who speaks their language and openly validates their resentments. They also have a candidate at risk of a decisive defeat — one with the potential to dislodge the angry white male from the centre of American politics.

Change is coming. A study by the union-backed Economic Policy Institute predicts that the American working class will be majority non-white by 2032 — a decade earlier than the population as a whole. But with a disastrous, divisive showing in November, Trump could begin to usher the angry white male off centre stage.

Democracy Corps, a project of Democratic pollster Stanley Greenberg and consultant James Carville, both of whom are longtime students of white working-class voters, released a memo this week that is remarkably incautious about the 2016 election, stating that “America is about to experience a once-in-a-lifetime earthquake of an election”.

Hillary Clinton is beginning to emerge with the kind of lead you would expect in a country where more than 60 per cent of the electorate will be racial minorities, single women, millennials and seculars, and where the positive sentiment about the Democratic Party is nine points higher than for the Republicans.

If Greenberg and Carville prove to be correct, perhaps those white male voters can continue to dominate a few more midterm elections, when the electorate is older and whiter than during presidential years.

But in the event of a Trump fiasco in November, Republicans will be looking for answers to a demographic problem for which none of the answers is “white male”. Even if the party freezes in place, incapable of making necessary changes, or fractures altogether, the result will be a diminished GOP, not a restoration of white male power.

And if the party finally begins diversifying its coalition, white males will have to learn to share the big tent. Trump’s racially polarising campaign, and celebration of crude machismo, will make that more difficult. But no matter the course Republican politics takes, it is hard to see how angry white males can remain the party’s abiding focus. Growing constituencies will need care and feeding. The half-century masculine scream that began with a hard-hat riot may finally begin to fade under the administration of the first woman president.

• Francis Wilkinson writes on politics and domestic policy for Bloomberg View