Donald Trump at Monday's presidential debate. Patrick Semansky/AP/Press Association Images. All rights reserved.15 months ago, when Donald J. Trump descended the Trump Tower escalator to launch his presidential campaign, he appeared to bring American civility down with him.

Announcing his intention to run, Trump called large numbers of Mexican immigrants rapists. Then, once on the campaign trial, he loudly condemned the esteemed veteran John McCain for having been a prisoner of war, and he mocked a journalist with disabilities. Trump also insinuated that tough questioning he received at a Republican candidate debate occurred because one of the moderators was menstruating. He later demanded that all Muslims be temporarily banned from entering the country.

Trump repeatedly flouted the conventional etiquette of American electioneering throughout the primaries – and his supporters rewarded him with victory after victory, culminating in Trump becoming the Republican Party’s designated nominee.

As the general election got under way, Trump occasionally acted in a more decorous manner, reading a speech or two from teleprompters, and holding a diplomatic briefing with Mexican president Enrique Peña Nieto. But the episodes of conventionally appropriate conduct have been overshadowed by Trump’s inflammatory insults and boorish comments. He attacked the parents of a fallen Muslim soldier and suggested that violence may be the best response to the election of his opponent, Hillary Clinton. And in the initial presidential debate, Trump reportedly interrupted Clinton 25 times in the first 26 minutes – a benchmark that is remarkable even in a forum where sharp-elbowed contention is expected.

How should we understand Trump’s behaviour? It is true that Trump seems to be provoking a crisis in civility. Yet it is also true that this is hardly the first time that American civility has been attacked.

As historians of civility have noted, generations of Americans have felt threatened by escalating incivility and they had no trouble finding causes in their own time. At different points during the twentieth century, Americans chalked up the deterioration of public conduct to jazz music, World War I, the Great Depression, World War II, the Vietnam War, the Civil Rights Movement, rock and roll, and the large-scale entry of women into the workforce. Nineteenth-century Americans blamed the Civil War, new immigrants, urban life, the vulgar rich, and the insolent poor. Talk of social crisis and fear of coarsening relations was also common in the eighteenth century. James Madison along with many of the Founding Generation complained about the truculence and crass materialism produced by the grasping, interest-ridden politics in the states.

Bouts of incivility regularly erupt. The difference across history is to be found in what opponents of civility at a given time believe they have to gain from their rudeness.

Consider the conflict over appropriate public behaviour that lay at the heart of the Civil Rights Movement in the twentieth century. Following the end of Reconstruction, a network of Jim Crow laws established formal racial segregation throughout the former Confederacy. These laws were surrounded and sustained by rules of racial etiquette that relegated African Americans to a subordinate position. Dr. Martin Luther King Jr. described what “proper” treatment of blacks looked like under these rules: “your first name becomes ‘nigger,’ your middle name becomes ‘boy’ (however old you are) and your last name becomes ‘John,’ and your wife and mother are never given the respected title of ‘Mrs.’” King rejected this code of conduct and demanded that African Americans be shown the same signs of respect as whites. From the perspective of those steeped in the old racial etiquette, King’s demands were gross violations of good manners that were to be sharply criticized and quickly suppressed. King and other “outside agitators” were castigated for being ill mannered and for refusing to keep to their appropriate station in the racial order.

Trump’s rudeness also has an objective. Polls show that nearly one-third of voters believe Trump’s supporters are actually “worse people than the average American.” Through his spectacular breaches of decorum, Trump has demanded that his denigrated followers be recognized and esteemed. As he thundered at the Republican convention, “I am your voice!”

Trump often scorns the equal measure of consideration that ‘political correctness’ bestows on the historically marginalised. This is not because Trump claims there should be no standard of respect in public discourse, but because he insists that the standard must be re-calibrated to elevate those groups that have not been given a place in the pantheon of politically correct pieties. As one white Trump supporter complained to BuzzFeed, “it seems like every other ethnicity” gets “a free card to say whatever they want and be completely accepted.” Trump seeks to reverse the polarity of public discussion. “When Mexico sends its people, they’re not sending their best,” Trump told his cheering crowd. “They’re not sending you.”

We often think of civility as a standard of decency that exists outside of politics and that is meant to restrain and pacify our disagreements. But Trump’s attempts to reconfigure civility should remind us that good manners have long been a subject of political struggle and debate. Courtesy and politeness are not simply given. They are instead modes of behaviour that are developed and perpetually refashioned through public dispute.

To achieve and sustain a civility that serves everyone, we must advocate inclusivity through our speech and model it in our actions. Like any advocacy in a free society, the push for egalitarian civility will generate pushback. And a successful campaign today will not prevent the need for further work from arising tomorrow. The effort will nonetheless be worthwhile if it can stop exclusionary versions of civility from gaining ground.