These are their stories — two decades worth of them.

As NBC’s “Law & Order: Special Victims Unit” returns Sept. 27 with its two-part premiere, fans of the New York City drama are eager to know what badass lieutenant Olivia Benson and company are up against in Season 20. Non-fans may ask, “Why is that show still on the air?”

It’s a valid question. As it turns the Big 2-0, the series — which averaged 8.9 million weekly viewers last season — shares bragging rights as the longest-running prime-time drama with “Gunsmoke,” a classic western, and the original “Law & Order,” whose straight-up title speaks for itself. Yes, 20.

So why has “SVU” and its harrowing tales of sexual assault, domestic violence and child abuse stood the test of time? The answer, Moneyish found, is a one-two knockout punch: Hard-to-watch stories plus an easy-to-love star equals stunning “SVU” staying power.

Mariska Hargitay, who’s played Benson since day one and now produces and directs episodes of “SVU,” shared her take on her on show last week at a Tribeca TV Festival event celebrating the program. “Very early into the shooting of the series and airing of the series did I learn how powerful talking about these issues would be in society,” said the 54-year-old actress, activist, wife and mother.

Seated between show creator Dick Wolf and fellow actor Ice T, Hargitay waved her hands like semaphore flags as she addressed the capacity crowd. “I gesticulate,” said the Emmy-winner, who had reason to be excited. “We’ve brought something that is traditionally swept under the carpet,” she said, “something that has left survivors in shame and in isolation … to the water cooler and a public arena in a way that has been profound and done a lot of healing.”

And the show did this way before the subject became the mainstream conversation it is today. “‘SVU’ was #MeToo before there was a #MeToo,” Matt Roush, TV Guide senior TV critic, told Moneyish. “‘SVU’ came on the air looking like the (‘Law & Order’) mothership’s unsavory cousin, but now looks like it’s going to break the original’s 20-year record — because for all of its sordid subject matter, there’s something almost comforting about the formula, about the catharsis of bringing these awful sex crimes to light.”

“SVU” also transcends entertainment. It has encouraged women and men who’ve been abused to seek help. “It has been an important way for survivors to know we exist and can support them,” said the spokesman for Safe Horizon, a victims assistance organization. (According to the Rape, Abuse & Incest National Network, an American is sexually assaulted every 98 seconds; only 310 out of every 1,000 sexual assaults are reported to police, the organization estimates.)

Ashlee Austin, 27, who teaches phys ed and health to Bronx high school students, looks to the show for classroom inspiration. “I use it as a teaching tool,” she said, adding that we need to talk about the fact that “these things can happen.”

For all its pluses, ‘SVU’ has its flaws. It frequently kicks nuance to the curb. “Sometimes it’s just the most lurid of melodrama — and (that) would be my biggest issue with the show,” said Roush. “It tends to go over-the-top in plotting.”

But even when “SVU” loses it, the star at the center of its universe is rock-steady, according to TV experts and fans.

“The importance of Mariska Hargitay as the anchor of the series is beyond measure,” said Roush. Reaching Season 20 “is all due to her loyalty to the show,” he added, “her diligence to put Olivia through the wringer season after season and still keep fighting the good fight.”

Onscreen and off. Hargitay founded the Joyful Heart Foundation in 2004 to help survivors of abuse heal. She’s made eliminating the nation’s rape kit backlog a personal crusade.

The high-profile fusion of Olivia Benson and Mariska Hargitay — Benitay, perhaps — is a mighty force. Asked why “SVU” has lasted so long, Tribeca audience member Kati Lampa, a 35-year-old Brooklyn premed student, answered without a heartbeat of hesitation. “Mariska Hargitay,” she said. “She’s the special sauce.”

Whatever the reason, SVU may soon become the longest longest-running prime-time drama in history: “Every year is a potential funeral, but hopefully there’s gonna be a new baby in September. That’s the goal. Nobody, until very recently, had a goal of exceeding 20 (seasons),” creator Wolf told the audience. “But that will happen. I’m fully convinced.”