TUCSON — Around the time that Donald J. Trump unofficially clinched the Republican nomination for president last May, he carved 10 minutes out of his schedule for an interview on “The Green Line,” an obscure podcast by the union of Border Patrol agents that was making its debut on a local talk-radio station.

For Mr. Trump, who had only to bellow his build-a-wall cry to stir his supporters into a frenzy, the interview offered a distinctive opportunity. He could take unchallenged digs at President Barack Obama while direct-selling his hard-line vision of border security to the very agents whose job it is to secure the border.

“I have you 100 percent in my mind and I have your back, believe me,” Mr. Trump told them on Episode 77, released on May 15, 2016. “You are incredible people and we are with you 100 percent.”

Until then, “The Green Line” sounded more like a mix of water-cooler banter and office bulletin board, where grievances on pay, leadership, uniforms and untrustworthy bosses were streamed online for internal Border Patrol consumption.

Interactive Feature | Excerpt From a Greenline Podcast Episode

The banter is still there. But the interview with Mr. Trump — on the heels of the union’s endorsement of him, its first in a presidential primary — amplified the podcast’s reach and profile, turning it into an influential, unfiltered and entirely one-sided political megaphone.

“We’re not going to apologize for what we believe in,” said Shawn Moran, the podcast’s original host and a vice president for the union, known as the National Border Patrol Council.

In 148 episodes (and counting), Mr. Moran and a recurring cast of agents-turned-union officials have criticized journalists, protesters, civil rights groups, Mr. Obama, the Mexican government, progressives, the “Hollywood elite” and anyone else they say has stood in the way of agents trying to do their job as they believe they should — including the leadership of the Border Patrol.

“Our managers now are turning around and saying, ‘You cannot call them illegal aliens,’” Art Del Cueto, a vice president in the national council, griped on Episode 125, released on Dec. 15. “They’re illegal aliens, that’s what they are, and we’ll say it all day long on The Green Line.”

The hosts have persistently criticized the polygraph tests that are required of anyone who is applying to become a border agent, saying they take too long, are often confrontational in tone and fail far more people than similar tests carried out by other federal agencies.

They have labeled reporters who cover topics in a way they do not approve as activists. Chris Cabrera, vice president of Local 3307 in Texas’s Rio Grande Valley, once accused Jorge Ramos, the Univision anchor, of having a vendetta against Mr. Trump. Fox News correspondent William La Jeunesse, on the other hand, has received warm welcomes in his appearances on the show.

They have also railed against the Obama administration’s hierarchy of priorities that forced border and immigration agents to focus on only deporting serious criminals. Then, they celebrated the new hardline attitude by Mr. Trump.

“It’s a good time to be a Border Patrol agent right now,” the union’s president, Brandon Judd, said on Episode 143, released on March 9. “One thing that President Trump did that no politicians had done previous is he kept the conversation on the border.”

Mr. Del Cueto, who is also president of Local 2544, which represents 3,000 agents in the Tucson Sector, the Border Patrol’s largest regional division, replied, “He’s definitely kept his foot on the pedal.”

The union’s foray into podcasting began in July 2012, when it launched “State of the Union,” which focused on work matters.

“State of the Union” eventually merged into “The Green Line,” whose first episode came online on Sept. 23, 2014. Six months later, the podcast gained a major sponsor, Breitbart News, the conservative-leaning organization with an outsize influence in the Trump administration; its former executive chairman, Stephen K. Bannon, is a chief strategist to the president.

In the early days of “The Green Line,” Mr. Moran said he recorded episodes from hotel rooms, his patio and “every Starbucks within five miles of my house.” These days, he records and edits them from the Breitbart News studios in San Diego, though the production can still have an amateur feel. Sometimes, one can hear the ping of a text message landing on a host’s cellphone.

On Tuesday, when it came time to work on Episode 148 — the main theme, again, was the polygraph test — Mr. Moran was ready. He had worked on radio before, as a disc jockey, back when he was studying criminal justice in the mid-1990s at the University of Scranton, in Pennsylvania, not far from his hometown Raritan, N.J.

Mr. Del Cueto, his counterpart in Tucson, was born in Mexico and brought up in Douglas, Ariz., which is just on the other side of the border. His mother is Mexican, his wife is Mexican and Spanish is the language he speaks at home, he said.

“I’m not anti-immigrant,” he said in an interview. “But my job is to catch the people who think it’s O.K. to break the law to come into this country, and I’m not cool with that.”

He took his position inside his office here, in a squat building with no sign near a Domino’s Pizza and a Walmart. He slipped on a pair of headphones and bobbed his head as a guitar riff from Pearl Jam’s “Jeremy” played into his ears.

Then, his lips began to move in silence, mimicking the words of Colonel Jessep, Jack Nicholson’s character in the courtroom drama “A Few Good Men” — the podcast’s opening salvo: “Because deep down in places you don’t talk about in parties, you want me on that wall. You need me on that wall.”

Mr. Del Cueto believes in a border wall. “I lock my front door not because I hate the people outside, but because I love the people inside,” he said.