“American Idol” Season 15 winner Trent Harmon, right, with host Ryan Seacrest and runner-up La’Porsha Renae in April 2016. (Kevork Djansezian/Getty Images)

As soon as Trent Harmon showed up to audition for “American Idol” in 2015, he sparked a debate among the judges about what type of music he was singing.

“Country,” Keith Urban said gleefully, as Harmon performed a haunting rendition of “Unaware” by Allen Stone.

“He’s not country,” Jennifer Lopez shot back. “He’s an R&B singer.”

Harry Connick Jr. stayed out of the argument but declared Harmon was his “favorite audition since we started.” Connick Jr.’s admiration proved prophetic, as Harmon, 25 at the time, became a fan favorite and won the show during the singing competition’s “farewell season” on Fox.

Everyone knows what happened next, as ABC scooped up the rights to the reality series, which airs its Season 16 finale on Monday night. As the reigning “Idol” champion, Harmon found success in the country music world. He released his debut album, “You Got ‘Em All,” last week — and his journey proves why thousands still try out for the show, even as it’s far from its heyday in the mid-2000s.

While detractors like to boast they can’t name an “Idol” winner since Kelly Clarkson, the show remains influential in Nashville. All three of the finalists this season could easily be country singers. And it doesn’t matter that Harmon started moving in the country music direction only at the encouragement of “Idol” mentor Scott Borchetta, president of Big Machine Label Group, where Harmon got a record deal. After he won “Idol,” doors flew open, even if his sound was also a mix of soul and pop.

“People love genres. . . . They have to put [music] in something to classify it, so their brain can understand, ‘What is it that I’m listening to?’” Harmon said. However, thanks to his built-in “Idol” fan base, people in Nashville didn’t seem to care how he classified his music.

Before auditioning for “Idol,” Harmon had been splitting his time — and barely making ends meet — between playing gigs in Nashville, his hometown in Mississippi and Arkansas, where he went to college. After his victory, he was able to land songwriting sessions with some of Nashville’s top talents.

“I used to walk into publishing houses before, and all I could ever do was get in the front office and hopefully shake hands with somebody,” Harmon said. “Now I’m going in there to write.”

Trent Harmon stops by “American Idol” Season 16. (Eric McCandless/ABC)

His first song released to radio, “There’s a Girl,” written with Laura Veltz and Jimmy Robbins, hit the Top 20 on the radio charts. His current single is the emotional “You Got ‘Em All,” a song he initially had no desire to write.

It was written the day after his longtime girlfriend told him that she planned to move out of the country for work. Harmon had a co-write scheduled with Justin Ebach and Jordan Minton, but he called Ebach to cancel. “I’m not in a good space to write,” Harmon started to explain. But when Ebach heard the story, he said, “You’re 100 percent going to write today.”

It proved therapeutic, as “You Got ‘Em All” is about how it feels if an ex stole all of your “better days.” The song is climbing the country radio chart and is currently at No. 38.

Harmon’s debut album is populated with other co-writes from hit Nashville writers, including “Her,” which explores the trappings of sudden fame. And, of course, a reminder of his roots: The record includes his cover of Sia’s “Chandelier,” which brought the house down on “Idol.”

And although Harmon would have loved to have had his album out more quickly, given the “Idol” Season 15 finale was two years ago, he discovered it was more important to build a cohesive body of work than capitalize on his newfound name recognition.

“You don’t get two first albums. . . . you want it to count. And, honestly, I didn’t have any songs,” Harmon said. “Now, I got to write the majority of the record. That means a lot more to me, and I know it’s going to mean a lot more to fans.”

Read more:

Scotty McCreery is too nice to gloat about his first No. 1 song. Here’s why he should.

Remember the name Ashley McBryde. Because after a decade, Nashville is finally paying attention.

After 15 years, Dierks Bentley finally feels established in country music. But he still wants to grow.