On July 20, 2012, Governor John Hickenlooper, of Colorado, was attending a friend’s seventieth-birthday party in Colorado Springs when he learned about a shooting in a suburb east of Denver. At 12:30 A.M., at the Century 16 movie theatre in Aurora, a young man wearing black body armor walked into the local première of “The Dark Knight Rises” and sprayed the audience with bullets; twelve people were killed and fifty-eight were injured.

At eight-thirty the following morning, Hickenlooper was ushered into a crime-scene trailer in the theatre’s parking lot, where officers showed him a video that they had taken inside shortly after the incident. A light on top of a handheld camera illuminated a scene of carnage. Bodies and popcorn and empty ammunition shells were strewn about the floor; pocketbooks and other personal belongings had been left behind in the rush to escape. “They were still in the process of removing the people who were dead,” Hickenlooper told me. “I mean, even the most hardened professionals were in shock. The scale and the madness of it—shooting seventy people.”

The alleged murderer, twenty-five-year-old James Eagan Holmes, was captured outside the theatre minutes after the police arrived on the scene. He used three guns, including a semi-automatic rifle with a hundred-round magazine, which jammed before he could empty it. Hickenlooper, a Democrat, had grown up around guns, and his relationship with the National Rifle Association was cordial. He was not convinced that any law could have stopped the killer. After the massacre, when asked if he supported new restrictions on firearms Hickenlooper said that it was too soon to discuss the issue. “If he couldn’t have gotten access to the guns, what kind of bomb would he have manufactured?” he responded to David Gregory, during an interview on “Meet the Press,” two days after the shooting. “We’re in an information age, where there’s access to all kinds of information, and he was diabolical.”

He has since changed his mind. By March of this year, a few weeks before President Obama’s firearms legislation was derailed in the U.S. Senate, Hickenlooper had signed three new gun-control laws that were among the toughest in the country, including a ban on high-capacity magazines like the one that Holmes used. The N.R.A. called Hickenlooper a “fanatic,” who was “only interested in pleasing Mayor Bloomberg.” Some Colorado conservatives have talked about initiating a recall.

“We weren’t in the right place to talk about it right after that shooting,” Hickenlooper told me recently, during an interview in his office, while his dog, Skye, an Akita-bulldog-Chow Chow mix, gnawed on a bone nearby. “But there’s so many of these shootings now that it seems like it’s always the wrong time.”

Hickenlooper, who is sixty-one, thin, and very tall, sat at a conference table hunched over briefing books. A few wisps of graying brown hair hung over his forehead. He likes to present himself as a political naïf—“I’m new to this game,” he often says, even though he’s been a politician for more than a decade, and he expressed surprise that the politics of guns is dominated by passionate activists who don’t always consider the facts.

“The N.R.A. and the advocates for no regulation really aren’t telling completely the truth when they say this is the beginning of losing your weapons,” Hickenlooper said, referring to the ban on large magazines, the most controversial law that he signed. “We’ve asked again and again for evidence of someone defending their home who needed more than fifteen rounds in a clip for a magazine. And you can’t find it!”

Hickenlooper, who campaigned as a governor who would appeal to all voters, has had some trouble keeping up with the political changes in his own state. Colorado voted for Republican Presidential candidates in three consecutive elections, from 1996 to 2004. But an influx of young liberals drawn to the mountains, retirees from the Northeast, and a growing Latino population—now twenty per cent of the electorate—has made Colorado increasingly Democratic. Obama won the state in 2008 and 2012, and the state House and Senate are both controlled by Democrats.

Colorado is part of a national trend: red states are becoming redder and blue states are becoming bluer. According to the National Journal, an unprecedented thirty-six states are controlled by one party or the other. Activists, frustrated by the partisan gridlock in Washington, are pushing their agendas in state capitals that are dominated by a single party and thus can swiftly move legislation. Two weeks before Hickenlooper signed his gun laws, the Republican governor of South Dakota signed legislation allowing school employees to carry firearms. In April, Kansas passed one of the most restrictive abortion laws in the country, while in Democratically controlled New York, Governor Cuomo unveiled a bill to guarantee in state law the protections provided by Roe v. Wade.

Hickenlooper began his tenure as a sensible centrist. But, instead of emphasizing the issues on which he campaigned—budget reform and economic development—he has found himself addressing a range of liberal social issues: gun control, civil unions, and a new law legalizing marijuana. A top aide summed up Hickenlooper’s first two years as “guns, gays, and grass.” He has learned the same lesson in Colorado that Obama learned in Washington: sooner or later, a politician has to choose sides.

Hickenlooper, until his mid-thirties, lived a wayward bachelor’s life. In the nineteen-seventies, he spent almost ten years at Wesleyan University, in Connecticut, earning an undergraduate degree in English and a master’s in geology. He took time off to teach math and science at a Quaker high school in Maine, and geology to college students in Costa Rica. He got engaged, broke it off, and, after an attempt to become a writer, ended up in Colorado, in 1981, as a field geologist for an oil company. He fell in love again, got engaged again, and broke it off again. He made beer in a dormitory bathtub and smoked a fair amount of pot, although, he told me, “I could easily say that, for quite a long time before I became mayor, I had obeyed all laws.” When I asked him about how he handled pot in Colorado—I was referring to the state’s new law—he joked, “I’ve always felt that you have to get the joint rolled really tightly.”

In 1986, during an energy bust, he was laid off, with a sizable severance package. During a visit with his brother in Berkeley, California, he enjoyed a life-altering beer at the Triple Rock Brewery, one of the pioneers of the microbrew fad. In Denver, he raised money with the help of family and friends, and, in 1988, opened a pub, the Wynkoop Brewing Company, in an area of abandoned warehouses called Lower Downtown. By the nineteen-nineties, as other restaurants and condos moved into the LoDo district, Wynkoop had become highly profitable. At the peak of his restaurant career, Hickenlooper owned sixteen pubs and restaurants around the country. According to his tax returns, he was making almost a million dollars a year when, in January, 2001, he met Helen Thorpe, a writer (and a former contributor to The New Yorker). They were married in January, 2002, and their son, Theodore, was born the following July.