Arnold Schwarzenegger, who is nearly 70 years old, probably thought his next battle would be against a mutant menace in a dystopian summer tent-pole film or an attempt to talk sense to some fool climate-change denier — and not a Twitter spat with the leader of the free world.

But as the whole world knows by now, that’s precisely what happened following Schwarzenegger’s debut as the new host of The Celebrity Apprentice. When the ratings came in lower than those of his predecessor, Donald Trump, the then-president-elect, struck out trumpily. “Wow, the ratings are in, and Arnold Schwarzenegger got ‘swamped’ (or destroyed) by comparison to the ratings machine, DJT,” Trump tweeted. “So much for . . . being a movie star — and that was season 1 compared to season 14. Now compare him to my season 1. But who cares, he supported Kasich & Hillary.”

At the mention of Trump’s tweet, Schwarzenegger smiles that slightly dopey ski-instructor grin made famous in his less apocalyptic films, like Twins and Kindergarten Cop. With a haughty laugh, he recalls the advice he gave himself upon hearing Trump’s dis: “Don’t get into a stinking contest with a skunk.”

He’s just finishing a workout at Gold’s Gym in Venice Beach, his home gym since landing in Los Angeles back in 1968. Between sets, Schwarzenegger poses for pictures with Russian gym rats. When another one asks for a few tips, Schwarz­enegger teaches him a favored lifting method: Start with heavy weights and keep dropping the weight as you increase the reps. “You’re basically shredding the muscles, and they don’t know what to do,” he explains. “They have no choice except to panic and grow bigger.” He then stops to hug a geriatric fitness-nut woman, the same Gold’s regular he famously hoisted above his head in the 1977 documentary Pumping Iron.

Workout complete, Schwarzenegger digs into a bowl of oatmeal and mixed berries while contemplating a question being asked by world leaders everywhere: How to handle The Donald.

Schwarzenegger has known Trump casually for decades and, in fact, volunteered to take his place on The Celebrity Apprentice. “I’d never done a reality TV show and thought it would be interesting,” he says. “When Trump started running for office, I said to myself, ‘Obviously he can’t do both.’ ” Schwarzenegger got in touch with Mark Burnett, the show’s creator, met with the brass at NBC, and was soon hired. “They said, ‘Let’s do a season and see what happens,’ ” he says.

In between, other things happened. Notably, Schwarzenegger announced that he could not vote for Trump and instructed other Republicans to “choose your country over your party.” After the tweet about Schwarzenegger’s ratings, it was clear that Trump had not forgotten the slight.

“I said, ‘Let’s sit on it for an hour,’ ” Arnold says, blowing on his gruel. Before long he had an idea. “I called my assistant and said, ‘I think what we really should do is request a meeting and go back to New York.’ ” He pauses for maximum impact. “ ’And then we just smash his face into the table.’ ”

Schwarzenegger’s laugh fills the cafe like a small nuclear explosion. He rubs his massive hands together. “And then I think we can’t do that, either. I think I have to be above all of that and put him on the spot.” He wound up tweeting a reply: “There’s nothing more important than the people’s work. I wish you the best of luck, and I hope you will work for ALL of the American people as aggressively as you worked for your ratings.”

Schwarzenegger has since maintained a guerrilla war against Trump — hey, Michael Bay, movie idea! — first chiding him for appointing a climate-change denier to head the Environmental Protection Agency, then ripping him for the botched rollout of an executive order banning travelers from seven predominantly Muslim countries. “It’s crazy,” the former two-term governor of California said during an appearance on Extra TV. “It makes us look stupid.”

“I think people really reacted well to that response,” Schwarzenegger says, pointing out that it’s Trump who sounds like a rogue action hero with no impulse control. “I sound more presidential and more diplomatic and more elder statesman — that’s exactly the way Donald should be.”

He disappears a mound of berries and arches his eyebrows. “And I should be the other way.”

The “other way” is the way that most people still think of Arnold Schwarzenegger: an 80-foot-tall, big-screen action hero and stogie-smoking satyr. He’s the guy who did a documentary on Carnaval in Rio that includes the profound comment, “After watching the mulattoes shake it, I can absolutely understand why Brazil is totally devoted to my favorite body part: the ass”; ran over Barbara Bush with a toboggan at Camp David; and blew up his marriage to Maria Shriver by fathering an out-of-wedlock son with the family maid.

But you don’t see much of that Arnold anymore. He’s undergone a middle-age transformation and now stands as one of America’s highest-profile environmental activists. He earned those credentials during six years as the governor of California: He built some of the state’s first hydrogen-fueling stations and issued executive orders to make thousands of existing government buildings energy friendly and new ones green certified. But that’s all small stuff compared with 2006’s California Global Warming Solutions Act, a groundbreaking first-in-the-nation piece of legislation designed to reduce the state’s emissions to 1990 levels by 2020. And all of this was accomplished as a Republican governor working with an overwhelmingly Democratic legislature.

“Arnold was a crucial voice from the right to say that tackling climate change was good for the economy, public health, national security, and environmental protection,” says Terry Tamminen, a longtime environmentalist and author who served as the head of California’s EPA under Schwarzenegger.

And Tamminen is not surprised that Schwarzenegger is just as passionate now. “He sees how California’s example can influence the world — especially the idea of not waiting for your national government or international institutions to take action,” Tamminen says. “We can’t wait.”

To hammer home that idea, Schwarz­enegger jetted to Paris in 2015 for the United Nations climate change conference, where he spoke about the emission-reducing pacts he inked, as governor, with Mexican states and Canadian provinces. Once the selfies were over, he addressed the assembled grandees: “The cities, states, and provinces are the best insurance policy because local policies can control 70 percent of emissions.” And he wasn’t afraid to lean on his big-screen persona to get the point across: “It is our moment to pick up the torch of a clean-energy future, in the cities and the states and in the provinces, and march forward relentlessly, like a Terminator.”

All of this sets up Schwarzenegger as a near-perfect foil for Trump’s retro support of coal and fossil fuel. Schwarzenegger will never seek office again; the only one he desires is the presidency, a constitutional impossibility for the Austrian-born actor. Instead, he plans to speak loudly and carry a big Conan sword.

At his core, Schwarzenegger is a savant when it comes to promoting. He started his career hawking nutritional supplements before hawking his movies globally, taking an active role when he thought the studio smoothies were dropping the ball. A major challenge in the fight against climate change, he says, is bad marketing.

“Environmentalists give speeches that sound really great to me, but to the ordinary folks they don’t mean anything,” he says. “You can talk about oceans rising and all that stuff, but, I mean, it doesn’t really translate to someone in Iowa who is struggling to put food on a table.”

Schwarzenegger understands that people are frightened by ISIS, homicides — all the scary things they see on television. So he’s decided to use his own scare tactics. In November, he created a 90-second public-service announcement pointing out that, worldwide each year, 7 million people die as a result of pollution — far more fatalities than from wars, car wrecks, murders, and suicides combined. The money quote of the video — which has garnered nearly 50 million views — is reserved for politicians who either move too slowly or, even worse, refuse to move at all. “I would like to strap their mouths on an exhaust pipe of a truck and turn on the engine and see how long it would take for them to tap out,” he says.

“This impacts people every day, right now,” he tells me. He sighs. “You have to talk about now. And if you don’t communicate it the right way, it will go right over people’s heads.”

Schwarzenegger’s Santa Monica office feels more like a theme-park attraction than a place of business. Life-size mannequins of Mr. Freeze and the Terminator serve as sentries. There’s an original Remington, and a scaled version of his Harrier jet from True Lies hangs from the ceiling. A giant bust of Lenin — a relic from the fall of the Soviet Union — hides behind a door. Then there’s what Schwarz­enegger’s aides call his Forrest Gump mantle: Arnold with Ronald Reagan, Arnold with Bush the Elder, Arnold with Bush the Younger.

But off to the side of his giant desk is a room that requires a special ticket. It’s a portal to Arnold’s childhood, a perfectly rendered Austrian dining room of the 1950s, when he was just a boy growing up in a country populated by fathers ravaged by military service to Hitler’s dark fantasies and worried about the Reds camped out in nearby Hungary. The room’s shelves are lined with beer steins and figurines, and the chandelier is made of deer antlers, an aesthetic choice popular in Austria. “I like it,” Schwarzenegger says. “It just reminds me of where I came from and how far away I am now.”

It’s true that no one loves Arnold like Arnold loves Arnold. But it’s also true that Schwarzenegger’s trajectory gives validity to the claim of his 2012 memoir that his is “the greatest immigrant success story of our time.” Born in 1947 in the small town of Thal, he was the second, less-favored son of Aurelia and Gustav, a policeman. Gustav was a shattered soldier who managed to survive World War II largely because a spinal wound suffered on the Eastern Front saved him from the destruction of the war’s final years. Clearly suffering from post-traumatic stress disorder, Gustav doted on his firstborn, Meinhard (who would die at 25 in a car accident), but beat Arnold for the smallest of offenses.

Schwarzenegger gives his father a generational pass. “Those who were in the war were affected deeply, not just because they lost but also because of the tremendous amount of punishment that a man goes through in those battles.” He stares out the window into the California morning light. “What happened to me happened to other kids.” He crushes some almonds and tosses them back. “I didn’t feel like, ‘Oh, I’m getting treated differently.’ ”

Always athletic and muscular, Schwarz­e­negger was 15 when he began lifting weights, after noticing how much luck bodybuilders seemed to have with girls. At the movies he watched Reg Park, the bodybuilder turned Hercules, and thought, “I’d like to do that someday.” In 1965, while serving in the Austrian army, he went AWOL to compete in the Mr. Junior Europe contest, which he won. It was not the first indication that the military was not a great fit. His father had called in a favor to get his younger son assigned to the tank corps, a move that Arnold paid back by (1) backing his tank into a wall (2) charging his tank down a hill, almost running over infantrymen and (3) falling asleep in a tank after forgetting to switch on the parking brake, causing the tank to slide into a pond.

Schwarzenegger continued to compete in — and win — European bodybuilding contests. In 1968, he made his first trip to the United States. He was invited by U.S. bodybuilding legend Joe Weider, who helped him get established in Los Angeles. It was the beginning of a 50-year love affair with California. “When people talk of going to America,” he says, “they don’t talk about Kansas. They talk of California.”

Schwarzenegger’s handsome looks and bulging torso helped take bodybuilding from freak show to something featured on network television. Not that any of his success in the Golden State was guaranteed or seemed even remotely possible. The director James Cameron, a friend of Schwarzenegger’s for more than three decades, remembers one of the first times he spoke to him, before making 1984’s The Terminator.

“How much acting experience have you had?” Cameron asked.

Schwarzenegger thought for a moment before answering. “It does not matter,” he said. “I intend to be a movie star like Clint Eastwood and Sylvester Stallone.”

“I’m hearing this and thinking, ‘Dude, that is so unlikely,’ ” Cameron recalls. “It’s basically like saying, ‘See this lottery ticket I just bought? I’m gonna win.’ ” Cameron laughs. “Yet once you know Arnold better, you know he just makes things happen.”

By now Schwarzenegger and I are in an SUV stuck in traffic on the Santa Monica Freeway. It’s January, and the sun is shining. To the right, a giant billboard for The Celebrity Apprentice looms high above the road. But Schwarzenegger doesn’t seem to notice, instead letting the sun settle on his chronically bronze skin and bronze hair. “When people built the studios, they didn’t build them in Iowa or Pennsylvania or in Florida,” he says. “They built them here.”

He rolls down the window and raises his arm up toward the sky. “I mean, why live anywhere else?”

Of course, just when you think you’ve got it all figured out, lounging raja-like in your cigar tent outside California’s statehouse, that’s exactly when the gods piss in your oatmeal with mixed berries.

It was January 2011, and Schwarzenegger was completing his second term as governor. This was something few Californians, including Arnold himself, ever could have imagined. But in 2003, California was in chaos. Voters had successfully petitioned the state to recall Democratic Governor Gray Davis, and more than 100 people — including Larry Flynt and Gary Coleman — entered the race to replace him. Schwarzenegger, who had grown tired of seeing his beloved state fall deeper in debt, announced his surprise candidacy during a taping of The Tonight Show with Jay Leno.

Once he got to Sacramento, Arnold got things done. He battled with then President Bush for millions of dollars for after-school programs and did his best to bring the overwhelmingly Democratic legislature’s prodigious spending into line with the state’s dwindling revenue. And then there was his work on behalf of the environment — specifically, climate-saving policies that also were business-friendly. “I made it clear that the oil wells that were out in the ocean and by our freeway . . . they were the past,” Schwarzenegger says. “Solar panels and the electric cars: This is the future.”

“Being a Republican allowed him to show that it wasn’t a choice between the environment and the economy,” says Fran Pavley, a Democratic state senator who worked closely with Schwarzenegger. “Now we have 100,000 solar-related jobs in California.” In a not-so-subtle dig at our current chief executive, Pavley says, “He wasn’t afraid to have people who knew more than him advise him. And he wasn’t vindictive if you disagreed with him.”

Sure, it wasn’t all Camelot. The state’s budget spun out of control after the 2008 recession, and Schwarzenegger was pilloried for forcing state employees to take unpaid days off. There was a failed attempt to pass a universal health care plan (though Schwarz­enegger claims that was an inspiration for Obamacare). And at home, his battles with the unions sometimes did not sit well with his wife. Shriver, who after all is the daughter of Eunice Kennedy and Sargent Shriver, the Peace Corps founder and 1972 Democratic vice-presidential nominee. His in-laws loved Arnold, but they were staunchly pro organized labor and were not amused when, for example, Schwarzenegger called Democratic legislators “girlie men” for not cutting state pension benefits.

Still, as his second term drew to a close, Schwarzenegger felt that he’d left the state in a better place. Not that he had any time to enjoy his accomplishments.

In a marriage-counseling session shortly after Schwarzenegger left office, Shriver revealed that she knew he had fathered a child with the family maid in 1997. She filed for divorce, and he was largely cut off from the Kennedys, his surrogate American family — who among other things had taught him how to argue politics over the dinner table, something forbidden back in Austria. What made the situation all the more unseemly is that Shriver had stood by her man when allegations of groping had threatened to derail Arnold’s first campaign.

It’s now six years later, and Schwarzenegger says he’s repaired the damage with his children and has a healthy relationship with his newly acknowledged son, who attends nearby Pepperdine. But he swears he doesn’t dwell on the greatest mistake of his life.

“You do think about it every so often,” he says, “and I can beat myself up as much as I want — it’s not gonna change the situation. So the key thing is, How do you move forward? How do you have a great relationship with your kids?”

It’s the only instance in our time together when Schwarzenegger seems eager to change the subject. “You can’t go back — if I could, in reality, be Terminator, of course I would go back in time and would say, ‘Arnold . . . no.’ ” He smiles a sad smile. “You know, it’s always easy to be smart in hindsight. That’s not the way it works.”

But that was then. Now, Donald Trump is in charge and Arnold Schwarzenegger is not ready to make nice. He’s prepping for a talk with students at the Schwarzenegger Institute for State and Global Policy at the University of Southern California, which he endowed in 2012 to promote bipartisanship. He swears that his disputes with the president are environmental, not personal.

“I’m just too much of a person that sees the threat of pollution and the environmental problems we have,” he says, explaining why he could not endorse Trump. “I felt like his approach of, ‘We are gonna bring coal back’ and all of this . . . ” He pauses for a second and just raises his palms upward. “I mean, c’mon! I cannot support going back to the Stone Age — it would be turning my back on everything that I’ve worked on.”

At the same time, Schwarzenegger holds a special place in hell for an unlikely foe: fellow environmentalists who fail to see the big picture. He talks of the Sunrise Powerlink, a system first proposed in 2005 to ship solar power from California’s Imperial Valley to San Diego. Environmental groups loved the idea in theory. Then they got the specifics. “I said, ‘OK, here’s the plan: We’re gonna build it from here to there.’ They said, ‘Whoa, whoa, whoa. . . . It goes through the national forest here, and then it goes through the desert, and then there’s the tortoise, and then there’s the sheep and then it goes through this Indian burial ground,’ ” he says.

Schwarzenegger loses his temper, shaking his head in disbelief. “They fought us for five years before we could start building it. And then seven years after we started, it was built. Why? We could’ve built the fucking thing in one year!” I’m now slightly frightened. “Just shut the fuck up and let us build green energy!”

Not that Arnold himself is eco-perfect. When I ask him what he drives, he admits he has a Yukon and, yes, a Hummer. His publicist groans. Schwarzenegger is quick to add that it is a biodiesel Hummer. “It smells like french fries,” he insists.

Hearing Schwarzenegger get animated, it’s easy to understand what his appeal was to Californians as governor: He’s Donald Trump with the green thumb and minus the black heart. “He probably thinks, ‘Man, I would be doing such a better job than that asshole,’ ” says Cameron. “There’s a certain parallel there, which is the cult of personality. People followed the cult of personality when they put Arnold in office in our state, and it worked out. I mean, was he the messiah? No, but I think it’s pretty manifestly obvious that the cult of personality with Trump has started us down the primrose path to hell.”

Schwarzenegger does a good job of hiding his external rage, reverting to humor as often as possible. He made a video with Cameron that talks about cutting down on beef consumption, since cattle production is a major climate killer. (Arnold still eats the sporadic steak.) He plays off his action-hero persona as he walks blindfolded through a methane-warmed desert almost stumbling off a cliff. He takes off his blindfold and says, in his trademark accent, “Less meat, less heat, more life.”

Now, sitting around a table with students at USC, he mixes the comedy act with real advice on bringing the eco-fight to a doubting public. An undergrad tells him her major — mechanical engineering — and starts into a question, but then she blushes: “I had something else to add, but I forgot.”

Arnold doesn’t miss a beat. “That’s OK. This is what happened to Governor Perry when he was running for president.”

Everyone laughs, but Arnold turns serious. “If you talk about beetle-infested trees or ocean levels rising 20 years from now, people say, ‘Well, that’s not really what I’m concerned about,’ ” he says. “People say, ‘What I’m concerned about is what is happening today.’ When environmentalists say ‘global warming,’ they miss the main issue. The main issue right now is that 7 million people worldwide die every year because of pollution.”

He urges the students to concentrate on the now, something he tries to do, even as he approaches 70. In the next week, there’s a trip to Austria to watch a pro ski race, a meeting with Pope Francis — Arnold tweets that he’s a “huge fan” — and more sniper shots at Trump over the travel ban.

Things got testy again in February when Trump inexplicably took a shot at Schwarz­enegger at the National Prayer Breakfast. “I want to just pray for Arnold if we can — for those ratings,” he said. A few hours later, Schwarzenegger replied: “Hey Donald, I have a great idea: Why don’t we switch jobs? You take over TV because you’re such an expert in ratings, and I take over your job and people can finally sleep comfortably again.”

Still, life hasn’t changed much for Schwarz­enegger. He recaps his recent schedule. “I was in China for two weeks doing a movie with Jackie Chan. I go right after that to Europe and do a speech. I come back and then, you know, shoot The Apprentice.” Plus, there’s a new movie coming out. It’s called Aftermath, and it’s about a man whose wife and child are killed in an airplane crash.

This being Arnold, his character goes after the air traffic controller he blames for the accident.

By now, Schwarzenegger has finished up with the students and is heading home to his Brentwood estate, with its guard station and steep driveway. His security detail and his beloved minihorse Whiskey greet him.

“My pony loves to come in the house and roam around,” Schwarzenegger says, waving to her in the driveway.

He climbs out of the car in the California twilight and is immediately surrounded — by his assistant, his security guy, and a production crew there to tape an interview. Arnold Schwarzenegger has just one question on his mind.

“What’s next?”

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