Army Capt. Humayun Khan was 27 years old when he was killed in Iraq.

On June 8, 2004, Khan was serving near Baquba when a vehicle packed with explosives approached the gates of his base.

Khan moved toward the suspicious vehicle while warning his soldiers away.

The vehicle exploded.

Khan was killed.

His actions were credited with protecting his fellow soldiers, and he was posthumously awarded the Bronze Star and Purple Heart.

Twelve years later, his parents walked onto the stage of the Democratic National Convention.

What followed became one of the most memorable confrontations of the 2016 presidential campaign.

A Gold Star Father Takes the Stage

On July 28, 2016, Khizr Khan stood before the Democratic National Convention in Philadelphia with his wife, Ghazala, beside him.

They introduced themselves as the parents of Capt. Humayun Khan and as “patriotic American Muslims with undivided loyalty to our country.”

Khizr Khan spoke about immigrating to the United States and raising three sons here.

Then he turned directly to Donald Trump.

Trump had proposed temporarily barring Muslims from entering the United States.

Khan argued that had such policies been in place when his family immigrated, his son might never have had the opportunity to serve the country for which he ultimately gave his life.

Then Khan reached into his jacket.

He pulled out a small copy of the United States Constitution.

“Have You Even Read the United States Constitution?”

Holding the Constitution in his hand, Khan addressed Trump directly.

“Have you even read the United States Constitution?”

He offered to lend Trump his copy.

Khan told Trump to look for the words “liberty” and “equal protection of law.”

Then he invoked Arlington National Cemetery.

He told Trump to visit the graves of Americans who had died defending the country, saying he would find people of different faiths, genders and ethnic backgrounds buried there.

Then came the line that would drive the controversy for days:

“You have sacrificed nothing and no one.”

The audience erupted.

But the story was only beginning.

Trump Responds

Two days later, Trump responded during an interview with ABC's George Stephanopoulos.

Asked about Khan's assertion that he had sacrificed nothing, Trump disputed it.

“I think I've made a lot of sacrifices.”

Trump cited his work and business career.

He said he had created thousands of jobs and built successful businesses.

Stephanopoulos pressed him.

Were those sacrifices comparable to what Khan was talking about?

Trump maintained that they were sacrifices.

But it was Trump's comments about Ghazala Khan that transformed the disagreement into something much larger.

“Maybe She Wasn't Allowed to Have Anything to Say”

Ghazala Khan had stood silently beside her husband during his convention speech.

Trump drew attention to that silence.

He said:

“If you look at his wife, she was standing there. She had nothing to say.”

Then he added:

“She probably, maybe she wasn't allowed to have anything to say.”

The implication was widely understood as a reference to the Khans being Muslim.

Trump noted that other people had raised similar questions.

But Ghazala Khan had a very different explanation for why she hadn't spoken.

A Mother Explains Her Silence

Ghazala Khan said she hadn't remained silent because someone prohibited her from speaking.

She remained silent because she wasn't sure she could speak about her dead son without losing her composure.

During the convention, a giant photograph of Humayun had been displayed behind his parents.

Ghazala later explained that simply looking at photographs of her son remained extraordinarily painful.

Seeing his enormous image behind her on the convention stage had been almost overwhelming.

She struggled simply to maintain her composure while standing there.

The following day, she responded publicly to Trump.

She explained that her silence had been the silence of a grieving mother.

“He Was Our Son”

The dispute quickly became about something larger than immigration policy.

Khizr and Ghazala Khan were a Gold Star family.

Their son had died wearing the uniform of the United States Army.

Trump was now engaged in a public argument with his parents.

Trump did acknowledge Humayun Khan's service.

In a subsequent statement, he called Capt. Khan “a hero to our country” and said Americans should honor those who made the ultimate sacrifice.

Trump also defended his immigration proposal, arguing that the United States needed stronger measures to protect itself from terrorism.

But he continued responding to Khizr Khan's criticism.

The dispute stretched across several days.

Republicans Become Uncomfortable

The confrontation put Republican leaders in a difficult position.

They could disagree with Khizr Khan's political criticism of Trump.

But criticizing the parents of a soldier killed in combat was another matter.

Republican National Committee chairman Reince Priebus said Gold Star families should be honored and suggested the Khans should be considered off-limits.

Other Republicans similarly distanced themselves from Trump's comments while emphasizing respect for Capt. Khan and his parents.

The controversy also came at a particularly sensitive moment.

Trump was no longer one candidate among many seeking the Republican nomination.

He was now the Republican nominee for president.

And he was publicly feuding with the parents of an American soldier killed in Iraq.

What Capt. Humayun Khan Did

Amid the political argument, the reason the Khan family was on that stage risked becoming overshadowed.

Humayun Khan had joined the Army through ROTC while attending the University of Virginia.

He eventually became an Army officer.

On June 8, 2004, he was serving in Iraq when a suspicious vehicle approached his base.

Khan ordered soldiers nearby to move back while he approached it.

The vehicle exploded.

He died protecting the people serving alongside him.

Khan was buried at Arlington National Cemetery with full military honors.

He received the Bronze Star and Purple Heart posthumously.

That was the sacrifice his father was talking about.

Two Very Different Definitions of Sacrifice

The confrontation ultimately produced one of the starkest exchanges of the campaign.

Khizr Khan spoke about his son dying while serving his country.

Trump responded that he too had made sacrifices, pointing to his work, businesses and the jobs he had created.

The two men were plainly using the word “sacrifice” in very different ways.

Then Trump's comments about Ghazala Khan expanded the controversy further.

Trump wondered publicly whether her religion prevented her from speaking.

She said grief prevented her from speaking.

Her son was dead.

She was standing beneath an enormous photograph of him.

And she was trying not to break down.

The Constitution in His Pocket

There were countless speeches during the 2016 presidential campaign.

Most disappeared almost immediately.

Khizr Khan's did not.

Part of the reason was the image.

A father whose son had died serving in the United States Army stood before millions of Americans and reached into his pocket.

He pulled out the Constitution.

Then he challenged the man seeking to become commander in chief to read it.

Trump could have responded simply by honoring Capt. Khan's sacrifice while disagreeing with his father's politics.

Instead, the argument continued.

Trump questioned whether Khan's speech had been written for him.

He compared his own sacrifices with those invoked by Khan.

And he publicly questioned why Ghazala Khan had remained silent.

That ensured the story didn't end when the convention did.

For days afterward, the Republican nominee for president found himself locked in a political dispute with a Gold Star mother and father.

At the center of it all was a young Army captain who never participated in the argument.

Capt. Humayun Khan had already given his answer about sacrifice twelve years earlier.