The Voices of Service quartet, including Caleb Green, left, who sings the national anthem at Washington Capitals games, performs on "America's Got Talent." Now in its 14th season, the NBC show is the rarest of summer phenomena: a hit. (NBC/NBC)

This season of “America’s Got Talent” has featured a rat that can navigate a New York cityscape, 76 Texas high-schoolers who kick as high as an oil derrick and a couple who throw knives at each other while singing opera.

However, the most impressive feat for NBC’s amateur competition series has little to do with the performers: It’s that 10 million people regularly watch it.

Broadcast ratings tend to plummet in summer, as fewer Americans stay home to watch TV. CBS’s much-hyped “Love Island,” starring beautiful strangers engaged in romantic melodrama, never managed to reach 3 million viewers for any episode this summer.

Yet “Talent,” which began its popular live-show episodes this past week, flies in the face of much of what experts know about the modern TV business. Adding to the achievement, much of the audience is in the coveted 18-49 demographic and also clicks on YouTube performances in massive numbers.

On Tuesday, the first of its live shows this summer, “Talent” notched 9 million viewers, the most of any program that night and more than double the 4 million of its main competition, ABC’s “Bachelor in Paradise.” On Wednesday, the show slipped somewhat, to 7.7 million, as it tends to do when it first expands to a second night in the summer. Still, the total was enough to easily win the night. The second episode of the reboot of “Beverly Hills, 90210” on Fox garnered just 2.6 million viewers.

“I’m not sure what to say,” said Howie Mandel, a longtime “Talent” judge, when asked for theories about the show’s popularity. “I guess viewers just like seeing ordinary people do extraordinary things.”

How the show has become a juggernaut is one of the entertainment world’s biggest puzzles, and no other network is sure how to solve it.

“You’re never going to beat it, but we still try every year,” said an executive at another network who spoke on the condition of anonymity so as to not reveal a loss of competitive advantage.

If you’re not familiar, “America’s Got Talent” is a vintage talent show done up with “American Idol”-style judging. It involves a host of acts — magic, singing, dancing, comedy — who compete in various rounds, with the goal of advancing to the live-show episodes in August and September. The winner nabs $1 million (albeit paid over a whopping 40 years) and performs at a variety show in Las Vegas.

A few have gone to bigger stages, such as magician Shin Lim, last season’s winner, who has since headlined a show in Vegas and appeared on Broadway. Recording stars are rarer.

Backstories are often highlighted and incorporated sentimentally into the performance. This year, one of the acts to make it through to the live show is Voices of Service, a group of military veterans who sing covers of Kleenex-yankers, such as Charlie Puth’s “See You Again."

The show was created by Simon Cowell, who launched a “Got Talent” franchise that would originate on the U.S. airwaves and eventually be exported to dozens of countries. (It’s produced by Fremantle, the reality juggernaut.) The show began as an also-ran of sorts on NBC in 2006, with a judging panel that included Piers Morgan and David Hasselhoff. But “Talent’s” first episode nabbed 12 million viewers. Its bona fides were quickly established.

This season, “Talent” has averaged nearly 10 million viewers in its two-hour Tuesday slot. Since it debuted in May, it has been the top show of the night nearly every time it’s aired, thanks to performers such as the knife-throwers (Nick & Lindsay), the dance troupe (Emerald Belles) and that rat act (Melissa Arleth and her crafty rodent Hanta).

This past Tuesday, the show’s 9.6 million viewers were nearly triple the number of ABC rival “Bachelor in Paradise” and almost five times that of “Love Island."

The show has recently experienced a slight ratings slip, averaging about 9.6 million viewers this year compared with about 10.4 million in 2018, although it could make up ground with the live shows. Relative to erosion for other shows, that slippage is negligible.

“Talent” has also held the line this year despite the swapping of several regular judges (Gabrielle Union and Julianne Hough replacing Mel B and Heidi Klum) and its host (Terry Crews replacing Tyra Banks). Mandel and Cowell remain the stalwarts at the judging table.

One of the keys to the success of “Talent,” executives say, has been its popularity across demographics.

“It’s the rare show that provides a co-viewing experience — my kids, who are 6, 4 and 2, watch it, my husband enjoys it, my parents enjoy it,” said Jenny Groom, executive vice president of alternative programming and development at NBC. “There’s a plethora of content nowadays that can divide people. Someone watches on their iPad, and someone is watching television, and someone else is watching on their laptop. This show brings a whole family together.”

There is, it should be said, some judging snark on “Talent,” but the show is way down the schadenfreude scale from the Cowell-era “Idol.”

To achieve the show’s unifying effect, producers scour the country for talent. They often take months on the road to find new acts.

“The goal is to find a new crop every year, to find things people haven’t seen before,” said Sam Donnelly, who executive-produces the show with Jason Raff.

“When we’re traveling to Chicago or Cleveland, we don’t know what we’ll find,” Raff said. “Many times it’s mediocre or boring.”

“Or weird,” Donnelly said.

“And then occasionally, someone comes into an audition room and dazzles us,” Raff said.

The tour happens in the fall, a full year and a half before the performances will be staged on-air.

NBC has practiced a kind of scheduling constancy with “Talent.” The network has resisted the urge to move the show to fall, a common practice for shows that do well in slower times. This past winter, for instance, Fox landed large audiences with the mystery musical show “The Masked Singer.” The second season will now debut in the higher-stakes fall season.

NBC’s Groom said there is no plan to move “AGT” out of the summer. Instead, NBC has used the rare phenomenon of a summer hit to launch new shows, such as the comedy-competition series “Bring the Funny,” which it has aired after “Talent” this year. The gambit has worked — somewhat. On Tuesday, the show lost about half the audience of “Talent,” though it was still enough to trounce the nearest competitor in the time slot by almost 2 million viewers.

But “Talent’s” big numbers may turn as much on familiarity as time slot.

“I think a lot of its success is about the consistency of format,” said Preston Beckman, a former strategist at Fox Networks Group and TV expert who goes by the online name the Masked Scheduler. “You cry a little, you root a little — there’s really not much more you need on television.”

There is something deeply old-fashioned about “Talent.” With its focus on everyday Americans and their brand of wacky earnestness, it evokes every high school talent show ever created and the vaudeville world that gave rise to them.

There’s also a decidedly of-the-moment quality to the series. Each act is custom-rigged to stand on its own; no set piece is given room to breathe beyond a few minutes.

“It’s the way people consume today, with all our limited attention spans,” Mandel said. “It’s, ‘If you don’t like something, hang in there 90 seconds and something new will come along.’ ”

Not for nothing has “Talent” become massive online. Clips can garner 5 million or 10 million views on YouTube. One performer this year, a blind and autistic pianist and singer named Kodi Lee, attracted more than 41 million views on the site.

Producers downplay virality as an endgame.

“I don’t think we’ve ever put on an act and said, ‘It won’t work on the stage but it will go viral,’ ” Donnelly said.

Still, she acknowledged it is part of the careful science of casting. “I think it’s that we look for the big moment onstage, and that happens to work well on social media,” she said.

The massive numbers have inspired envy — and competition.

Sometimes that has taken the form of a show in the same lane, as ABC tried with a revival of “The Gong Show.” It was canceled last summer after just two seasons, which averaged 2.7 million and 2.8 million viewers, respectively.

And, sometimes, as this year, it’s with a show that goes the other way, such as “Love Island,” which CBS deployed Tuesday nights in the hope of counterprogramming the sweetness of “Talent” with salaciousness. “Island” was recently renewed, but its 2.6 million average-viewer total won’t give “Talent” producers any night terrors.

How much longer NBC can keep this up, however, remains a question.

In this decade, a period of great turbulence for network television, “Talent” has averaged between 10 million and 11 million viewers in fully half the seasons, and has never gone above 12 million or dipped below 9 million average viewers. By contrast, “The Voice,” another NBC competition hit, has lost half its audience this decade, going from an average of nearly 16 million viewers when it first debuted in the early 2010s to just 8.7 million this season.

But even hit reality shows tend to degrade as they move through their second decade; “American Idol” began sliding off a ratings cliff after its 11th and 12th seasons.

“Talent” also has a more specific obstacle: It must keep one-upping itself in novelty. Most important, it has no control over the people who it must rely on to do that.

Future success, in other words, depends on just how increasingly audacious Americans are willing to get.

“That is the thing that keeps Sam and I up every single night, to be honest,” Raff said. “It gets harder and harder every year."