Republican presidential candidate Donald Trump speaks during a campaign rally on Thursday in Cedar Rapids, Iowa. (Evan Vucci/AP)

CEDAR RAPIDS, Iowa — On Thursday night, Donald Trump stood before a few thousand Iowans packed into a hotel ballroom and equated all Syrian refugees with Islamic State terrorists, while endorsing the use of waterboarding, which he considers a proven method that is "short of torture."

A thousand miles away in Philadelphia, two parents from Virginia stood on the stage of the Democratic National Convention and talked about the 2004 death of their 27-year-old son, Army Capt. Humayun S.M. Khan, who was serving in Iraq. They described themselves as "patriotic American Muslims with undivided loyalty to our country."

In both places on Thursday night, the vastly different crowds chanted: "USA! USA! USA!"

In a small town in eastern Iowa, Trump warned his mostly white audience that President Obama is already allowing thousands of Syrian refugees with "no real documentation" to pour into the country and that Hillary Clinton would increase that rate by "550 percent." As Trump spoke, the crowd cheered as the politician voiced their fears. A man in the crowd shouted: "Send 'em home!"

"You know what they do? They put them all over the country. Nobody even knows where they're being put, so we don't even know what's going to happen — but all we know is we watch these people with the slashings and the throat cuttings and the cutting off of the heads and the drowning in steel cages," Trump said, seeming to equate all refugees fleeing violence in their homeland to Islamic State terrorists.

He continued: "These are people, they have to be stopped. They have to be stopped. And they have to be stopped very, very strongly and very viciously, if we have to."

Campaign_2016_Trump-f1103 Supporters of Republican presidential candidate Donald Trump cheer as he speaks during a campaign rally in Cedar Rapids, Iowa. (Evan Vucci/AP)

Trump said that he would "absolutely" support bringing back waterboarding, which he described as an interrogation method that works and is "short of torture" and "minor." The crowd cheered this stance. When Trump criticized Obama for discontinuing the use of waterboarding because his administration deemed the technique torture, a man in the audience bellowed: "Lock him up!" Another shouted: "Waterboard Obama!"

"So, they can chop off heads. Right? They can drown people in steel cages. They can cut your throats. We can't waterboard," Trump said. "You know, we're playing by different rules, okay? We're playing by different rules. ... They can chop off heads. We can't waterboard."

Trump said the "beautiful world" Obama described at the convention Wednesday night does not exist.

"You know, his beautiful world," Trump said. "He doesn't talk about radical Islamic terrorism. He doesn't talk about the fact that people don't want to fly on airplanes and that people don't want to go to theaters. He doesn't talk about what's going on."

Across the country in a cavernous arena in urban Philadelphia, attorney Khizr M. Khan stood on the convention stage, his right hand carefully placed over his heart. His wife stood silently to his right, her hands folded on a corner of the lectern and her eyes communicating the same deep emotion that soon resonated in his voice.

"Like many immigrants, we came to this country empty-handed," Khan said. "We believed in American democracy — that with hard work and the goodness of this country, we could share in and contribute to its blessings. We were blessed to raise our three sons in a nation where they were free to be themselves and follow their dreams."

Humayun Khan was an American Muslim Army soldier who died serving the U.S. after 9/11. His father, Khizr Khan, spoke at the Democratic National Convention and offered a strong rebuke of Donald Trump, saying, "Have you even read the United States Constitution?" (Video: Victoria Walker/The Washington Post;Photo: Michael Robinson Chavez/The Washington Post)

Their son, Humayun, dreamed of becoming a military lawyer, but he was killed in Iraq in 2004 when a vehicle packed with explosives approached his compound in Iraq. He told his men to seek cover while he ran toward the vehicle, which exploded and instantly killed him. He was awarded the Bronze Star posthumously.

"Hillary Clinton was right when she called my son 'the best of America,' " Khan said. "If it was up to Donald Trump, he never would have been in America. 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."

Khan then demanded to know if Trump had read the U.S. Constitution, as he pulled his own copy out of his suit jacket.

"I will gladly lend you my copy," Khan said, thrusting it toward the cameras. "In this document, look for the words 'liberty' and 'equal protection of law.' Have you ever been to Arlington Cemetery? Go look at the graves of brave patriots who died defending the United States of America — you will see all faiths, genders and ethnicities. You have sacrificed nothing and no one. We can't solve our problems by building walls and sowing division."

Khan's remarks in Pennsylvania lasted just a few minutes, while Trump spoke for about 50 minutes in Iowa.

Trump brought up religious freedom toward the end of his remarks, thanking evangelical Christians for their support of his candidacy and promising to get rid of the Johnson Amendment, which bars religious institutions and tax-exempt organizations from endorsing or opposing political candidates.

"If you look at what's going on with religion — and this is religion, this isn't just evangelical, this is religion — but if you look at what's going on, it's not going in the right direction, because the ministers, the pastors, the rabbis, the people, this includes the Catholic, the priests, they don't have power to express their thoughts," Trump said.

Seconds later, Trump added: "And by the way, we will be saying 'Merry Christmas' again. Okay?"