It was a festive afternoon at the Sunset Cove Amphitheater. Families rolled out blankets on the lawn beside a man-made lake. Vendors sold foot-long hot dogs. Organizers tossed T-shirts from the stage.

Then, at nightfall, Donald Trump took the stage – and things turned dark.

“On Friday, we went to Chicago,” the billionaire presidential candidate told his supporters. They booed the mention of the Trump event that was canceled because of protests. “We had some, I would say they were – let’s be nice – ”

“(Expletives)!” a man near the front bellowed. The crowd laughed.

“Let’s call them protesters,” Trump suggested. The crowd booed.

Trump mentioned one of his opponents, Florida’s Marco Rubio. This produced a chorus of boos and insults: “He sucks!” “Deport him!” “Send him back!”

He mentioned another opponent, Ted Cruz. The crowd answered with a chant of “Lyin’ Ted!” and cries of “Liar!” and “He’s full of (expletive)!”

Trump mentioned Hillary Clinton. Audience members shouted: “(Expletive) Hillary!” “Put her in jail!” “Waterboard Hillary!”

He bemoaned the trade imbalance with China. One man rolled up his “Silent Majority Stands With Trump” sign and bellowed through it: “(Expletive) China!” The crowd chanted: “Build the wall! Build the wall!”

To get a better sense of the Trump crowds, I watched Sunday night’s rally here not from the penned-in press section but up front, in the crush of the crowd. I entered with the public and stood silently for four hours, running my digital recorder.

A couple of dozen people protested before and after the event, and a few people were removed during Trump’s speech because of shoving.

But it was relatively tame for a Trump rally, in part because Trump supporters fingered suspected infiltrators in the crowd and had them removed by private security guards before Trump spoke. In one of several such incidents I witnessed, Trump supporters signaled for security after a young man in a baseball cap who identified himself as “John” got into a political argument with some Trump fans. “Get him out!” one shouted.

“I didn’t say anything!” John pleaded as guards, taking the word of his accusers, led him away.

An announcement before events advises participants not to harm those who “have taken advantage of Mr. Trump’s hospitality.”

But Trump has sent a different message, declaring Sunday that he might pay the legal fees of a man who sucker-punched a demonstrator and then said his victim might need to be killed next time.

The crowd Sunday evening apparently purged suspected “disrupters” too thoroughly. “Do we have a protester anywhere?” Trump asked. Trump and his advisers seem to delight in the confrontations, which fuel the crowd’s energy.

Those around me were almost all white and mostly men.

Their T-shirts and caps said they were gun owners, veterans, Marines and Harley riders. I heard nothing racist or angry or paranoid in their conversations. But once Trump arrived, they became ominously transfixed and aggressive. They pumped their fists, flashed thumbs up, mouthed “Thank you,” chanted “Trump! Trump! Trump!” and hung on the candidate’s every word – often with looks of ecstasy and some visibly trembling.

Trump captivated them with words that were alternately desperate and violent: “Our country is going to hell. … We’re sitting on a very big, fat, ugly, bubble. … We’re like the lap dog for the world. … Drugs are pouring across. … They’re chopping off heads. … You see so many people being killed. … The jobs are being sucked out. … We’re losing with everybody.”

Before Trump spoke, a woman warmed up the crowd by reading tearfully from the autopsy report of her son, killed by an illegal immigrant (“slipknot around his neck”). “The media is in an uproar about the tone of Mr. Trump’s campaign,” she said, but not that “we’re burying our children every day at the hands of illegal aliens.” She accused Rubio of spending “blood money” and asked the senator which of his children he “would give up for a foreigner to have a nicer life.”

But happily for Trump’s supporters, deliverance was at hand. The orchestral theme from the movie “Air Force One” played, and a helicopter flew low above the Trump fans, who raised signs and fists heavenward.

Trump stepped out moments later to offer salvation. Twice he said that in a Trump presidency they could “relax” while he defeated the Islamic State and beat the world in trade.

“We’re gonna become rich again,” he promised. “We’re gonna become great again.”

From the passionate cheers sounding around me, I knew they believed him.

Dana Milbank is a columnist for The Washington Post. He can be contacted at:

danamilbank@washpost.com;