Donald Trump was speaking at an event in Iowa, complaining that America was not allowed to waterboard terrorists, when Khizr Khan and his wife walked up to the microphone at the Democratic convention in Philadelphia.

Khan's son, Humayun, was a captain in the U.S. Army. When a vehicle packed with explosives approached his compound in Iraq in 2004, he instructed his men to seek cover as he ran toward it. The car exploded, killing Khan instantly. He was awarded the Bronze Star posthumously.

In 2005, The Washington Post interviewed Khizr Khan. "They did not call him Captain Khan," he said of the men his son led. "They called him 'our captain.' "

"We are honored to stand here as the parents of Captain Humayun Khan," the elder Khan said at the Democratic convention, "and as patriotic American Muslims with undivided loyalty to our country." He spoke of his son's dreams of becoming a military lawyer and how Hillary Clinton had referred to his son as "the best of America."

Then he focused his attention on Trump.

"If it was up to Donald Trump, [Humayun] never would have been in America," Khan said. "Donald Trump consistently smears the character of Muslims. He disrespects other minorities, women, judges, even his own party leadership. He vows to build walls and ban us from this country.

"Donald Trump," he said, "you are asking Americans to trust you with our future. Let me ask you: Have you even read the U.S. Constitution? I will gladly lend you my copy." He pulled a copy of the Constitution from his pocket. "In this document, look for the words 'liberty' and 'equal protection of law.' " Earlier this month, Trump promised congressional Republicans that he would defend "Article XII" of the Constitution, which doesn't exist.

"Have you ever been to Arlington Cemetery?" Khan asked. "Go look at the graves of the brave patriots who died defending America — you will see all faiths, genders, and ethnicities.

"You have sacrificed nothing. And no one."

In Iowa, according to the Guardian's Ben Jacobs, Trump was talking about polls.