RIO DE JANEIRO — A live radio broadcast featuring a conservative Brazilian columnist and the Rio-based American journalist Glenn Greenwald devolved into a physical scuffle on Thursday, laying bare the extraordinary political polarization gripping Latin America’s largest country.

The issue at hand: accusations by the columnist, Augusto Nunes, that Greenwald and his husband, a Brazilian politician, weren’t taking proper care of their two adopted Brazilian children. The exchange was live-streamed on YouTube, video of which quickly went viral on social media.

“Who’s going to take care of the kids?” Nunes asks.

“Coward!” Greenwald calls him, again and again. He leans in closer and points a finger. “You are a coward!”

Then Nunes takes a swing at Greenwald.

The American swats it aside. The men stand — and Nunes slaps Greenwald in the face.

Others step in to pull the men apart, but Greenwald breaks loose and takes a swing at Nunes. He misses.

“What is this?!” someone off camera yells. “Calm down!”

People on the left rallied to the defense of Greenwald, the polarizing American journalist who came to prominence reporting on the U.S. government’s surveillance programs exposed by Edward Snowden. Those on the right cheered Nunes.

“Though I often disagree with his comments and independent of the facts cited, I stand in solidarity with this man @agostonunes,” wrote Carlos Bolsonaro, son of the nationalist President Jair Bolsonaro.

Explosive reports published this year by Greenwald’s Intercept Brasil have deepened divisions in the country. The stories, drawing from a trove of leaked correspondence, cast doubt on the impartiality of the sprawling corruption investigation here known as Lava Jato, or Operation Car Wash.

One of the main targets of the leaks was Brazil’s Justice Minister Sérgio Moro, the judge who oversaw the bulk of the probe. The Intercept alleged that Moro had improperly counseled prosecutors on how to try their corruption case against Brazil’s former leftist president Luiz Inácio Lula da Silva.

Moro sentenced Lula to nine years in prison, clearing Bolsonaro’s main political rival from his path to the presidency. After Bolsonaro won, he appointed Moro as his justice minister.

Greenwald, long a fierce critic of Bolsonaro, has become one of the main targets of the right’s ire. Politicians called for him to be charged with a crime and deported. He now lives surrounded by armed guards inside a fortified house.

One frequent critic from the right was Nunes, a conservative newscaster and columnist.

Several weeks ago, Nunes made it personal on his show, attacking Greenwald’s parenting.

“I was thinking about this couple,” he said of Greenwald and his husband, David Miranda. “Glenn Greenwald spends the day having hissy fits on Twitter or working as the recipient of stolen messages. David is always in Brasilia. ... Who takes care of the children that they have adopted? This should be investigated by the juvenile court.”

Greenwald told The Washington Post that he learned that Nunes would be on the conservative panel show “Jovem Pan News” on Thursday and decided to confront him. He said he’d hoped that his appearance on the show would demonstrate a willingness to talk even with those who disagree with him.

But first, he said, he had to get some things off his chest.

He told Nunes his comments were “the most disgusting thing I’ve seen in my life.”

“I want to know if you believe if a minors judge should investigate our families with the possibility of the kids returning to the shelter without moms and dads and no family whatsoever.” he said. “Do you believe in that?”

Nunes turned away.

“First, you’ll see he can’t identify irony, a good-humored attack,” Nunes responded. “I only said that his companion spends all of his time in Brasilia, and he spends all of his time dealing with stolen material, and I was like, ‘Who’s going to take care of the kids.’ That’s it!”

“Coward!” Greenwald yelled.

Nunes didn’t respond to a request for comment. He defended himself in local media.

“I was morally insulted,” he said. “So I warned him not to use the word ‘coward;’ that is insulting and serious. I warned him five times, and he insisted. I had two options: reacting with a higher attitude or swallowing that insult. I had no alternative.”

He said he would do it again.

In a statement, he was more contrite.

“I regret that this occurred,” he said. “I ask listeners, viewers and readers not to make any political disagreements into physical acts, even indignation provoked by unacceptable rude behavior.”

Greenwald accused Nunes of homophobia and called his use of violence “fascism.”

“This endorsement of violence in our political discourse is fascism,” he said. “If they want him to hit me, why shouldn’t anyone on the right be allowed to hit anyone on the left in the streets?”

“That’s why this is so dangerous,” he said, “because of how polarized Brazil is.”

Heloisa Traiano contributed to this report.