“I don’t care how old you are,” Mayor Pete Buttigieg, of South Bend, Indiana, said at Tuesday night’s Democratic debate, in Detroit. “I care about your vision.” One of the CNN moderators, Don Lemon, had asked whether voters should “take into consideration age when choosing a Presidential candidate,” after helpfully pointing out that Buttigieg, who, at thirty-seven, is the youngest candidate, was standing next to Senator Bernie Sanders, of Vermont, who, at seventy-seven, is the oldest. It was one of a number of attempts by the moderators to get the candidates to confront or even just slight one another directly, such as when Senator Amy Klobuchar, of Minnesota, was asked whom on the stage she might have been comparing herself to when she said that she wouldn’t “make promises just to get elected.” (“Everyone wants to get elected,” she said.) Buttigieg, avoiding the crude insistence on youth that Representative Eric Swalwell, of California, who has since dropped out, indulged in during the previous debate, added, “You can have great Presidents at any age.” Sanders, as it happened, agreed with that.

But age was an image that Buttigieg deployed again and again, often deftly, sometimes as a metaphor, sometimes as a practical yardstick. Answering Lemon, he said that the particular vision he cared about candidates having was “one that can win,” which for him meant that it could not be “back to normal.” A sentence later, he used age to get at the related matter of legacy. There hadn’t been enough talk in the debate, he said, about President Trump’s “enablers” in the Republican Party, who, by deferring to him, were supporting “naked racism.” He then looked directly into the camera and said, “If you are watching at home, and you are a Republican member of Congress, consider the fact that, when the sun sets on your career, and they are writing your story, of all the good and bad things you did in your life, the thing you will be remembered for is whether, in this moment, with this President, you found the courage to stand up to him or continue to put party over country.” If Lemon had, in effect, asked viewers to consider how young Buttigieg is now, Buttigieg had turned the question around to ask Republicans of all ages to imagine themselves when they are very old, and in the land of regret.

And Buttigieg used his life span as a measure of the passage of time and the extent of political failures. “This is the exact same conversation we’ve been having since I was in high school,” he said, during an exchange about gun control. “I was a junior when the Columbine shooting happened”—when two students at a Colorado high school shot and killed twelve of their classmates and a teacher, injuring twice as many. “I was part of the first generation that saw routine school shootings. We have now produced the second school-shooting generation. We dare not allow there to be a third.” In other words, it was alarming to him that he had grown older than the problem; his own generational displacement only heightened the urgency of instituting at least minimal commonsense measures, such as effective universal background checks. On this topic, the distinctions among the candidates mostly had to do with whose commitment was the most sincere and long-standing. (Montana Governor Steve Bullock’s support for universal background checks was fairly recent; asked about that in Detroit, he mentioned that his eleven-year-old nephew, Jeremy, had been shot and killed in a playground.) “We know what to do, and it has not happened,” Buttigieg said.

Similarly, when Buttigieg was asked whether he would withdraw the remaining American troops from Afghanistan, where he was deployed in 2014, and where the first troops were sent in the months after the September 11th attacks, he said that, when he returned, “I thought I was one of the last troops leaving Afghanistan. I thought I was turning out the lights years ago. Every time I see news about somebody being killed in Afghanistan, I think about what it was like to hear an explosion and wonder whether it was somebody that I served with, somebody I knew—friend, roommate, colleague. We’re pretty close to the day when we will wake up to the news of a casualty in Afghanistan who was not born on 9/11.” (Trump, meanwhile, said last week, “I could win that war in a week. I just don’t want to kill ten million people.” He added that this victory would involve a “plan” in his possession for Afghanistan “to be wiped off the face of the Earth.” The remarks, understandably, caused an uproar in Afghanistan.)

The former congressman Beto O’Rourke, of El Paso, said that he would make a commitment to withdraw from Afghanistan in his first term, adding that he didn’t see how staying would “make it better.” John Hickenlooper, the former governor of Colorado, said that this approach would court disaster. But one of Buttigieg’s strongest points was that the authorization for the use of military force was one that Congress had approved a decade and a half ago, and that it has been stretched to cover deployments far from Afghanistan, too. No such vote has been called on the costs and benefits of further military engagement, whatever they may be, by the members of Congress who are accountable to this generation. “On my watch, I will propose that any authorization for the use of military force have a three-year sunset and have to be renewed,” Buttigieg said. Such authorizations must have a limited life span; otherwise, wars will grow too old for soldiers who were too young.

And there was another time span, which Buttigieg mentioned in both his opening and closing statements: twelve years, an estimate of the time left before we reach a climate catastrophe. “By 2030, we will pass the point of no return on climate,” he said, adding that by then there will also be a hundred and thirty million more guns on the street. “I’ll be in my forties then,” Buttigieg said. “If you have kids, think of how old they will be then.” They may even be ready to run for President.