(CNN) The first votes of the primary season were more than a month away but when Hillary Clinton was at the University of Minnesota in mid-December, she was already preparing to cast herself as the complete opposite of Donald Trump.

"To all our Muslim American brothers and sisters: This is your country, too," Clinton said. "And I am proud to be your fellow American."

Her comments came just a week after Trump shocked the country with a proposal to temporarily ban Muslims from entering the United States. Tucked into her remarks was the story of Army Capt. Humayun Khan, serving as a sharp rebuke of Trump's proposed edict. From there, interest in Khan's parents would place them on stage at the Democratic National Convention where a powerful speech would shake the political world seven months later.

Born in the United Arab Emirates, Khan had immigrated to the United States as a young boy and enlisted in the U.S. Army after college. Clinton described Khan's last day on earth: when a suspicious vehicle approached Khan's infantry in Iraq, he told his troops to get back even as he pushed forward. When the car exploded, Khan was killed on the spot, but his unit was unharmed.

Clinton, in her speech, cited Khan's father from a recent interview: "We still wonder what made him take those 10 steps," Khizr Khan had said. "Maybe that's the point, where all the values, all the service to country, all the things he learned in this country kicked in. It was those values that made him take those 10 steps."

Khizr Khan made his national debut on the stage of the Wells Fargo Center in Philadelphia with a stinging rebuke of Trump's worldview. His address sparked a turbulent week that threatened to overturn Trump's presidential campaign and demonstrates just how volatile the 2016 campaign has become.

Even Clinton aides and convention planners who described how the address came together said they never expected the response that would soon follow.

The backstory

The Clinton campaign became aware of Khan's story while preparing for her December speech in Minnesota. According to multiple aides, a member of Clinton's speech writing team came across a print interview where Khizr Khan described the 10 steps that his son, Humayun, took before his death.

It was immediately clear, aides said, how powerful Khan's story was.

"If you want to see the best of America," Clinton said, "you need look no further than Army Capt. Humayun Khan."

Shortly thereafter, Democratic Party representatives contacted Khizr Khan to ask if they could pay tribute to his son's memory at the party's mid-year meeting, Khan told CNN this week.

He agreed.

A few weeks later, the phone rang again. Party officials wanted permission to pay tribute to Humayun again -- this time, at the national convention in Philadelphia.

"Which father will disagree when someone says they will pay tribute to your son? I readily agreed," Khan said.

That decision was months in the making.

As Clinton's top aides -- communications director Jennifer Palmieri, senior communications adviser Mandy Grunwald and senior strategist Joel Benenson -- began to plan the programming for Philadelphia and what kind of "everyday Americans" could tell their stories, Khan's name emerged at the top of the list.

He would only have a few minutes to speak, Khan said he was told, but his wife urged him to take the opportunity. He wrote out six pages of prepared remarks, but when he read it out loud to her, she urged him to cut it down.

"You only have four minutes," Ghazala Khan told her husband.

"She's my editor, my program manager, my source of strength," Khan said on Tuesday.

The night of the speech

Khan submitted his speech to the Democratic National Committee representatives the day before he was set to speak, on the fourth and final night of the gathering. Those remarks were handed out to reporters before Kahn took the stage.

The Khans were were offered the usual precautions about getting through the heavy security at the Wells Fargo Arena: bring as little as possible to save time.

Khan pulled out the loose change and keys out of his pants pockets, and grabbed his suit jacket from the hanger. He didn't realize that his pocket Constitution was in the breast pocket. As an immigration lawyer, Khan carries the document around as often as he can.

The pages of the small booklet are wrinkled, and it is full of notes, highlights and underlined passages. Some of the pages in the Fourteenth Amendment -- his favorite part -- are loose, and Khan's markings there are heaviest.

On their way to the Well Fargo Arena, Khan asked his wife if he should use the well-worn copy in the speech.

"Can I pull it out?" he asked.

"Sure," Ghazala Khan responded. "When you're talking about something, this will be a good prop."

In the green room beforehand, Khan practiced pulling the Constitution out from his pocket over and over again. He wanted to make sure the audience and cameras could see the cover.

"Donald Trump: You're asking Americans to trust you with their future. Let me ask you: Have you even read the United States constitution? " Khan said on stage. He put his hand over his blue tie, and pulled out the worn booklet from his jacket pocket.

"I will gladly lend you my copy," Khan said, thrusting the Constitution into the air as the arena broke out into thunderous applause.

Trump's reaction

Clinton's aides watching inside their workspace in the Well Fargo Center and at campaign headquarters in Brooklyn, New York, recognized what a powerful moment Khan's speech was.

No one, aides said, expected Trump to respond the way he did.

"Who wrote that? Did Hillary's scriptwriters write it?" Trump said in an interview with ABC the following Sunday. "I think I've made a lot of sacrifices. I work very, very hard."

He added: "If you look at his wife, she was standing there. She had nothing to say. She probably -- maybe she wasn't allowed to have anything to say. You tell me."

The interview drew instant rebuke from Democrats and Republicans, including GOP leaders who said it was unacceptable for the party's nominee to go after a Gold Star family.

But rather than pull back, Trump doubled down.

"Mr. Khan, who does not know me, viciously attacked me from the stage of the DNC and is now all over T.V. doing the same - Nice!" he tweeted.

But the Khans also refused to back down.

After Trump questioned why she didn't speak, Ghazala Khan published an opinion piece in The Washington Post, explaining her silence on stage that night: "Without saying a thing, all the world, all America, felt my pain. I am a Gold Star mother. Whoever saw me felt me in their heart."

Speaking at a church in Cleveland on Sunday, Clinton said Khan "paid the ultimate sacrifice in his family."

Trump, she said, had "nothing but insults, degrading comments about Muslims" and "a total misunderstanding of what made our country great -- religious freedom."

Later that day, Clinton told reporters that the controversy questions where the "bounds" or the "bottom" is in Trump's campaign.

"I think this is a time," Clinton said, for Republicans "to pick country over party."