[WARNING: This story contains some plot spoilers.]

TORONTO — After mass shootings this year, Americans have been embroiled in a debate over the nature of the perpetrators and the factors that drive them.

Now Hollywood is about to weigh in.

This year’s Toronto International Film Festival has explored many fraught issues, from immigration to criminal justice to Nazis doing slapstick. But it has just surfaced perhaps its most charged topic yet: What propels someone to pick up a gun and begin killing complete strangers?

The film is “Joker,” and while it comes in the form of a comic-book movie, it is the very opposite of light.

"Set aside that it’s the DC [Comics] universe,” Cameron Bailey, artistic director of the festival, said in an interview. “Just think of it as a great character study that goes really dark.”

Toronto is the first major proving ground for “Joker,” which Warner Bros. brought to the festival in the hope of launching a commercial release and awards run. In the process the film has begun to emerge as one of Hollywood’s most potentially explosive movies in years — a study of a man coming unhinged, carrying out random acts of deadly violence and igniting a populist revolution.

“Joker,” which will be released in theaters Oct. 4, has proved to be divisive. And not just because of the traditional range of aesthetic opinions but because of what the movie represents and which political groups will commandeer it — the Hollywood release as political weapon.

The movie focuses on the pre-Joker Arthur Fleck — a sad-sack clown slowly unraveling under his troubles in early -1980′s Gotham — before he starts finding solace in a gun and mask and becomes a folk hero in the process. It stars Joaquin Phoenix and is improbably directed by Todd Phillips, the filmmaker behind the "Hangover” comedies.

The stakes are high for Warner Bros., whose DC Extended Universe has struggled to land phenomena at anywhere near the consistency of Disney’s rival Marvel Cinematic Universe (with only one release, “Aquaman,” of more than $1 billion in global box office to Marvel’s nine).

That “Joker” won the Golden Lion at the Venice Film Festival just a few days ago — Warner Bros. is the first major Hollywood studio in the modern era to win the prize — ups the ante. The victory leapfrogs the company ahead of Disney, which earlier this year became the first studio to notch a best picture Oscar nomination for a comic-book movie (“Black Panther").

With a relatively modest $55 million budget and a large marketing campaign planned, “Joker” is an attempt to notch one for the AT&T subsidiary as it seeks to compete with the market leader.

But the talk at this festival, which more than any other gathering sets the tone for Hollywood’s all-important Oscar season to follow, shows that the stakes are a lot higher than even the battle for corporate bragging rights.

Some commentators have vigorously decried “Joker’s” message. Time’s Stephanie Zacharek wrote that Phoenix’s character “could easily be adopted as the patron saint of incels,” she wrote, referring to the “involuntary celibates” group of frustrated males whose beliefs have come up in several mass killings.

“In America, there’s a mass shooting or attempted act of violence by a guy like Arthur practically every other week. And yet we’re supposed to feel some sympathy for Arthur." The film “lionizes and glamorizes” the character, she wrote. She concluded that “there’s a sick joke in there somewhere. Unfortunately, it’s on us.”

Zacharek and those who disagree with her view have been confronting the essential questions surrounding the movie: by peering so closely at a killer, is Phillips trying to understand his mind or glorify his thinking? Indict the mental-health system that failed him or cheer that he broke free from conventionality?

At the post-screening party Monday night, a debate broke out among journalists and industry executives over whether the movie could become part of the texts cited by potential future mass shooters, and what that would mean. Even if the causation between media violence and the real-world shootings is statistically unproven, a few asked, couldn’t the movie still become part of the problematic context for them?

Warner Bros is understandably eager to play down any such talk. That’s in part because the current climate has led rivals to cancel movies — Universal Pictures, most recently, scrapping “The Hunt” after last month’s shootings in Ohio and Texas. Any future tragedies could lead to similar pressure on Warner.

But it’s also because the studio is no stranger to the debate about the relationship between superhero-villain violence and the real-world kind. The company was behind the release of “The Dark Knight Rises” — the movie that was playing at an Aurora, Colo., theater when a gunman opened fire in July 2012, killing 12 people. The shooter cited the movie as an intentional choice.

Warner may have little ability to quell the speculation, though. At the Venice premiere, a moviegoer approached Phillips and said he thought Paris would burn as a result of the movie. Phillips maintains that the goal is not to make Fleck a hero, especially as the character’s actions become more violent. He simply has chosen to make a gritty movie that uncommonly focuses on a villain.

“How do you make a movie with white face and green hair and run it through as realistic [a] lens as possible?” Phillips said after the screening. “Because we don’t believe you fall into a vat of acid and are turned that way,” he said, referring to what the comic books say about how the Joker character was created.

Those with a long memory have also been recalling the moment 30 years ago when two reviewers warned that Spike Lee’s conclusion of “Do The Right Thing,” in which a black character tosses a garbage can through the window of a white-owned pizzeria and sparking a violent confrontation with police, was “dynamite under every seat,” as Newsweek’s Jack Kroll said at the time. David Denby of New York magazine even wrote that Lee would be partly responsible “if some audiences go wild."

That moment has since become an example of cringeworthy mischaracterization of, and overreaction to, social violence on screen. Warner executives are eager to make the comparison too.

In case none of this seems timely or charged enough, the film could plunge itself into the 2020 presidential election.

One theory, already advanced by liberals, is that the Joker shares commonalities with President Trump, fueled as he is by a brittle ego and a love of performing and crowds. (A subplot involves Fleck, an aspiring comic, pining for an appearance on a popular late-night show). Phillips and co-writer Scott Silver wrote the movie in 2017, shortly after Trump took office, so the camp could make a case for the timing.

Meanwhile, the revolution Fleck’s actions unintentionally set off — an eat-the-rich mob unleashes and tries to overthrow the banking system — is fraught with political symbolism. What kind, though, is unclear. The mob could be viewed as either Republican Trump voters or, at the other end of the spectrum, anti-Wall Street progressives. And that, in turn, will likely weaponize the movie politically — both the right and the left can use it to demonstrate bad acting by the other side.

“There is something for bad people to admire here, but there is also a lot of things people can use to say what’s bad about the other side," said one industry member, speaking on the condition of anonymity to avoid the appearance of weighing in on the film.

From the moment the screening ended, the debate was on over whether Phillips had made a brilliantly inscrutable work or, less favorably, a movie as elastic as its protagonist’s face. People could agree on only one thing: “Joker” is coming, as unavoidable as a clown mask.