It’s not a secret: a surefire way for a presidential contender to get votes is to promise to increase the defense budget. It has worked for nearly every president since John Kennedy—and it worked for Donald Trump. Back in September 2016, candidate Trump promised he would not only increase the Pentagon’s budget, he would add more soldiers, sailors, and airmen (and women) to the military’s ranks.

In April, Trump followed up on his pledge by signing a defense bill that not only ended the spending caps, but called for an increase in the military’s size in 2018 by adding 20,000 new personnel—including 7,500 more soldiers, 4,000 more sailors, 1,000 new Marines, and 4,100 more airmen.

Senior military officers, and particularly Army Chief of Staff Mark Milley, celebrated the increase. Since becoming his service’s senior officer, Milley has argued that to meet its obligations, the Army will need 540,000 soldiers in its ranks by 2022, an increase of some 70,000 soldiers over four years. “It is not some arbitrary number,” Milley told a gathering of Army veterans back in August. “We have done the analysis. We need to be bigger, and we need to be stronger and more capable.”

Milley’s goal meant that the Army not only needed to find 17,500 new soldiers every year, it needed to find replacements for those who retire or leave the service every year—about 20 percent of the force. So it is that the Army set its 2018 recruiting goal at 80,000 soldiers. Initially, at least, Milley’s target seemed modest, reachable. It wasn’t.

In April, the Army revised that number—downwards. Instead of recruiting 80,000, it announced that it would recruit 76,500 new soldiers. But even that number might be too high, as the Army notes that it’s recruited only 28,000 in the first six months of the year.The problem, it seems, isn’t that young people don’t want to join the Army—or any of the services—it’s that they can’t.And therein lies a paradox: for while the U.S. military represents the best in America (as its most senior officers claim), it doesn’t actually represent America. For that to be true, two thirds of our military would have to consist of obese, under-educated former drug users and convicted criminals.

Here’s the arithmetic: one in three potential recruits are disqualified from service because they’re overweight, one in four cannot meet minimal educational standards (a high school diploma or GED equivalent), and one in 10 have a criminal history. In plain terms, about 71 percent of 18-to-24-year-olds (the military’s target pool of potential recruits) are disqualified from the minute they enter a recruiting station: that’s 24 million out of 34 million Americans. The good news is that while the military takes pride in attracting those who are fit, educated, law abiding, and drug-free, they’re having difficulty finding them—manifestly because fewer of them actually exist.

Then too, of the pool of remaining potential recruits, only one in eight actually want to join the military, and of that number, fully 30 percent of those who have the requisite high school diploma or GED equivalent fail to pass the Armed Forces Qualification Test (the AFQT), which is used to determine math and reading skills. Tutoring companies produce sample tests and there’s an “AFQT for Dummies” on the shelves. Here’s a sample question: “Five workers earn $135/day. What is the total amount earned by the five workers?” Put more simply, the purpose of the AFQT isn’t to identify the most qualified, but to winnow out the illiterate, the 30 percent who can’t read, write, or count, despite their high school diplomas.

That’s why the numbers are grim: “There are 30 some million 17 to 24 year-olds out there, but by the time you get all the way down to those that are qualified, you’re down to less than a million young Americans,” Marine Corps Major General Mark Brilakis says. In fact, Brilakis might be overestimating the number—if only one in eight of 10 million in this age group actually want to join the military, that leaves a pool of 1,250,000 potential recruits. If 30 percent of those can’t pass the AFQT, that number becomes 750,000.

In addition to winnowing out recruits due to mental, physical, and social ineligibility, there’s a natural cap to the pool. There are, after all, perfectly good reasons why young Americans might not want to serve: the military is regimented, physically demanding, sometimes boring and often dangerous. “When you sign up for the military you don’t just sign up for a new job,” retired Colonel Kevin Benson, a West Point graduate and former director of the Army’s School of Advanced Military Studies, notes. “You’re really joining a new culture. It’s a way of life. Not surprisingly, when many potential recruits realize what they’re getting into they decide to do something else.”

There are a number of possible solutions to the military’s recruiting crisis. The services could lower their eligibility requirements, assign more recruiters to focus on target populations, lower the numbers of military members the armed forces needs—or all three. But lowering standards is not in the cards. “The recruiting numbers look bad,” a retired Army senior officer admits, “but I think the glass is half full. None of the services have taken the easy way out by lowering recruiting standards, and the result is that we have a smarter military than we’ve ever had.” This retired officer (who requested anonymity as he is in a sensitive position in the private sector), cited the impact of a legendary West Point “tank study” of the 1980s that showed smarter tank gunners are actually more accurate tank gunners—that, in effect, smarter soldiers are better soldiers. It’s not simply that smarter recruits are more capable of operating sophisticated weapons systems (like the F-35); they’re better fighters, too, which is, after all, the whole point.

The services have responded to the recruiting crisis by recasting their recruiting strategies. The Navy’s new multimillion dollar “Forged by the sea” appeal is a dual promotion that focuses on what the Navy offers while telling “Gen Zers” what the Navy actually does—an important point, as it turns out, because, according to the ad firm that proposed the appeal, most young Americans don’t actually know. It’s a heavy lift: the Navy will have to retain its current numbers and add 11,400 sailors by 2019 and then increase that number again in order to fulfill the Trump administration’s plan to build a 355-ship fleet. The Air Force faces an even more daunting challenge: the service is 2,000 pilots short and, until recently, the numbers of its recruiters were historically low. It has increased retention bonuses, assigned additional recruiters (100 more this year), and reopened closed recruiting offices. But the tech-heavy service doesn’t just need increased numbers. It also needs more recruits for specific specialties: maintenance, cyber warfare, intelligence, surveillance, reconnaissance, and nuclear experts—that is, recruits who don’t walk in off the street.

In truth, the military isn’t just attempting to address a recruiting crisis; it’s also facing what the retired senior Army officer described to me as “a force structure design issue.” Put simply, the military needs more recruits to offset the continuing demands of the serial deployments that have marked the war on terrorism. An Army of 540,000 soldiers can sustain multiple fights in Afghanistan, Iraq, and Syria—an Army of 450,000 can’t. Then too, of course, there’s the unmentionable and unquantifiable challenge of recruiting young Americans to serve in wars that seem to go on forever. So the Army has rejiggered its recruiting numbers down because, at least in part, America’s next generation of soldiers are voting with their feet—they’re staying away.

This crisis isn’t new. Back in 2009, a group of retired military officers (including two former Joint Chiefs) started a “Mission: Readiness” campaign recommending that the U.S. government increase funding for local and state early education programs, arguing that “increased investments in high-quality early education are essential for our national security.” Their plea was unprecedented: they implied that the U.S. might better meet its national security threats by spending money on education programs instead of on weapons. “This is primarily a local and state initiative,” retired Army Lieutenant General Thomas Spoehr, the director of the Center for National Defense at the Heritage Foundation, says. Spoehr points out that “Mission: Readiness” has scored successes in selling the benefits of early education and fitness and nutrition programs in a number of local school districts.

Back in February, Spoehr co-authored a Heritage Foundation “backgrounder” recommending specific reforms to improve education and reverse “the downhill fitness trend.” The goal, as he described it, was to ensure that kids “stay in school, stay fit, and stay out of trouble.” Yet as Spoehr also reluctantly noted in a telephone interview, one of the challenges the military faces is that it recruits in states where America has the greatest fitness and obesity challenge—the Deep South. For while America’s soldiers, sailors, and airmen are educated, fit, and good citizens, they’re also religious, rural, conservative (80 percent of military personnel voted for Donald Trump), and Southern.

“I may have met two or three New Englanders when I was in the Army,” retired Colonel Kevin Benson told me, “but that would be about it.”

So while the U.S. military is ethnically and racially diverse (with increasing numbers of women), it’s not geographically diverse, even though military officers insist that they recruit everywhere. In fact, when pressed, senior military officers dismiss the notion that the military has a pro-South bias. “The military is Southern because that’s where the recruits are,” a career Army officer explains. That’s one explanation, but there’s another: perhaps the military is Southern because that’s where the military recruits. “Yeah, it’s a dilemma,” Spoehr admits, “because we really lack geographic diversity. But I don’t know exactly how we solve that.” Benson agrees, but argues that recruiters have little choice. “There’s a strong military tradition in the South, it’s where most of our military bases are located and the best ROTC programs are there,” he notes. “Besides, what are we supposed to do, say ‘no’ to someone who wants to serve?”

There was a time, and not so long ago, that a majority of senior military officers competed to name the gravest future threats facing the U.S. For many in the Army, facing down a revived European power, it was Russia. For the Navy, patrolling a vast expanse of the Pacific, it was China. For the Air Force, it was keeping up with endless deployments and aging fighters. For the Marines, it was “Iran, Iran, Iran.” All of those views are now being transformed. The gravest future threat to America, many senior military officers now believe, is that America might not be capable of meeting its gravest future threat. The basis for their view is that the military’s current recruiting crisis has provided them a window into a younger generation of Americans, those young men and women who will become the soldiers, sailors, airmen, and airwomen of tomorrow—but can’t.

Mark Perry is the author ofThe Most Dangerous Man In America and The Pentagon’s Wars. Follow him on Twitter @markperrydc.