A bookend to one of the most turbulent weeks in the presidency of Donald Trump, the death on Saturday of Republican senator John McCain of Arizona compelled a reckoning with how enraged and divided his party and his country have become.

“In an era filled with cynicism about national unity and public service, John McCain’s life shone as a bright example,” said the Senate majority leader, Republican Mitch McConnell of Kentucky.

No example shone more clearly than McCain’s rejection of the personal, and often ethnic, animus that has marked Trump’s presidency. In a moment played on loop since the death of the war hero and two-times presidential aspirant, the 2008 Republican nominee rebuked a supporter in Minnesota for saying that she couldn’t trust his opponent, Barack Obama, because he was, in her factually challenged words, “an Arab”. His rebuttal gained new traction a decade on as an example of McCain’s candour and decency, values captured in the name of his campaign bus, the “Straight Talk Express”.

But the Straight Talk Express sputtered during McCain’s first unsuccessful drive for the White House in 2000, when a controversy arose over the candidate’s use of an anti-Asian slur in South Carolina. At stake were questions of speech, memory, context, offence and apology — questions that today frame the country’s charged political moment.

The episode, little known compared with the “Arab” incident eight years later, sheds light on McCain’s identity as a veteran of a war that seared the nation; a maverick with a strong will and a short temper; and a committed yet imperfect unifier who aimed to diversify his party. The incident also marked the transition from a Cold War mindset that cast East Asians as an enemy to a political culture defined by the war on terror, in which Arabs loom large.

The candidate for the Republican nomination, who endured five years of torture in a North Vietnamese prison camp, came under criticism in February 2000 for using a racial epithet to describe his captors.

It wasn’t a gaffe. He had used it before on the campaign trail, although the slur went mostly unreported by the media. One notable exception was a September 1999 story in US News & World Report by Roger Simon, in which the journalist wrote: “Strictly speaking, one does not say ‘gooks’ any more. It is simply not done. But John McCain says [it] and who is going to tell him not to?”

Simon said the word frequently crossed the candidate’s lips, before voters and reporters alike. McCain had enlisted the epithet a dozen times in a first-person account of his imprisonment that appeared in Rolling Stone in May 1973. The derogatory term for East Asians was widely used by members of the United States military during the Korean and Vietnam wars.

At first, McCain was unrepentant, claiming the right to recall his jailers as he wished.

“I was referring to my prison guards,” McCain said, “and I will continue to refer to them in language that might offend some people because of the beating and torture of my friends.”

“I hated” them, he said, using the slur once more, “and I will hate them as long as I live”.

According to press accounts at the time, McCain made clear that his hatred applied only to his captors. Elected to the Senate in 1986, he was a leader of efforts in the 1990s to normalise diplomatic relations with Vietnam. And over the weekend, members of the Vietnamese community held a vigil outside of the late senator’s office, and Reuters reported that people in Vietnam left flowers at a monument by the lake where McCain was shot down in 1967.

Courtney Griffin tweeted “Vietnamese community holding vigil for #SenatorJohnMcCainoutside his office ...”

Still, the language was incendiary, and it drew the condemnation of the Vietnamese Government and of some Asian-Americans in the US — for whom the slur had racialised meaning that transcended McCain’s individual memory of his suffering at the hands of the North Vietnamese.

“John McCain’s words and statements, which lack goodwill, have hurt the Vietnamese and Asian peoples,” a spokeswoman for the Vietnamese foreign ministry said at the time. In an editorial, the San Jose Mercury News put matters bluntly. “No one expects the former POW to speak kindly of his torturers,” the paper observed. “But their sin was being sadistic thugs, not being Asian.”

The California primary was fast approaching.

By the end of the month, McCain had offered a full-throated apology and pledged not to repeat the epithet.

“I will continue to condemn those who unfairly mistreated us,” he said. “But out of respect to a great number of people whom I hold in very high regard, I will no longer use the term that has caused such discomfort. I deeply regret any pain I have caused.”

He concluded: “I apologise and renounce all language that is bigoted and offensive.”

Campaigning soon after in “Little Saigon” in Orange County, California, McCain drew several thousand political exiles and refugees who packed into a shopping mall parking lot to hear the decorated Navy veteran extol them as a community that “epitomises what America is all about”.

He would ultimately suffer a lopsided defeat in the primary to George W. Bush, who went on to win the nomination, and the presidency.

Simon, who was among the first to bring McCain’s language to light, told The Washington Post he was impressed by how the candidate dealt with concern over his unvarnished language.

“Today, you report something that causes a candidate difficulty and pain, and they verbally strangle you or send their henchmen to strangle you,” Simon said. “He didn’t complain about it. He owned up to it. And it’s not like he kicked me off the bus. He kept giving me interviews.”

For the journalist, it was a testament to the deference shown by the media to a candidate that gave them extraordinary access, combined with the deference shown to a war hero in recounting his torture. As Bob Dole, a former Republican leader of the Senate, reportedly put it: “You spend five years in a box, and you’re entitled to speak your mind.”

But was he? Maybe when the candidate was still a long shot, Simon said. As he started to “make more of a dent in the public consciousness”, he said, McCain’s speech was subject to more serious scrutiny, and it was found wanting.

The straight shooter appeared to learn from the incident, Simon said. He estimated that the apology was strategic, arriving shortly before a primary in a state with a sizeable Asian-American community, but he also said the candidate drew important lessons from the blowback.

“Certainly he learnt when to keep his mouth shut, and not to use racial slurs,” Simon said. “I also think it showed pretty early on that he wanted to maintain a certain amount of dignity in a process that does not reward dignity. It rewards the opposite.”

The clearest evidence that McCain learnt from his missteps in 2000, Simon said, might be his defence of his Democratic opponent in 2008. And in recent years, as the Republican Party diverged from the approach of its 2008 standard-bearer, McCain sought to remain steadfast in his break with “language that is bigoted and offensive”, as he put it. He condemned Trump’s denigration of Mexicans as “rapists” and accused the rhetorical bomb thrower of having “fired up the crazies”.

As for whose speech will ring out at his funeral, McCain requested eulogies from two presidents — George W. Bush and Barack Obama.

•Isaac Stanley-Becker is a reporter based in Britain