Throughout the current presidential campaign season, there have been repeated calls for free college. Channeling a long-held position by Sen. Bernie Sanders and his supporters, the Democratic candidate, Hillary Clinton, said that families making under $125,000 per year should be able to send their kids to college tuition-free. As someone who graduated college tens of thousands of dollars in debt, I am inclined to sympathize with this proposal. Student debt is a critical issue.

Opponents to Clinton’s proposal rightly cite the immense expense that these policies would impose on the federal budget. To date, however, a serious potential implication of free college for lower and middle income students has been ignored: the impact on military recruiting.

Higher education is rightly hailed as the surest path to the middle class. Because of its cost — both tuition and lost working hours — a college education has not been possible for everyone across the income spectrum. In a defining moment of the last century, the federal government enacted the G.I. Bill in 1944, providing returning American soldiers with the financial wherewithal to pursue a degree. It was, perhaps, the keystone policy for expanding the U.S. economy and creating the modern American middle class.

Mirroring higher education’s path to the middle class, military service remains one of the surest means to a college degree. In its latest form, the Post-9/11 GI Bill provides up to $20,000 per year for tuition. To compensate for time without an income, it also provides a living stipend adjusted for the local cost of living. For example, in Cambridge Massachusetts, where I attend graduate school, that stipend is $2,800 per month, which is pro-rated for when classes are in session.

Many of those who join the military do so, at least in part, to obtain access to the G.I. Bill and the financial means to obtain a degree. According to a 2011 Pew Research Survey, 75 percent of those who enlisted said they did so to obtain educational benefits. That statistic has risen from the pre-9/11 era when it was just 55 percent — likely because college has become that much more expensive! As of 2014, 48 percent of Iraq and Afghanistan veterans utilized the G.I. Bill, with 59 percent of female veterans doing so (a demographic the military wants to see grow in its ranks). If college became free, the incremental value of the G.I. Bill would be dramatically reduced. The effect would be similar for the Yellow Ribbon program, which provides money for education to those who have already served, ROTC scholarships, which provide funds to pay for a bachelor’s degree for aspiring officers, tuition assistance programs for those already on active duty, and the various programs to fund graduate education for officers. Without the G.I. Bill as a serious inducement to enlist, the military is likely to experience substantially more difficulty in recruiting new personnel. This will, with little doubt, require us to pay more to recruit tomorrow’s force and sustain the qualitative edge of our superb military.

The military’s ability to recruit is critical not only to its success but to the very existence of the all-volunteer force. If the all-volunteer military cannot recruit sufficient numbers of new personnel, it cannot survive. The number of new recruits the military needs varies with government policy and defense requirements. During the height of the Iraq War, it had so much difficulty recruiting — and with retaining personnel already serving — that it instituted the “stop loss” program. Under this policy, the military unilaterally cancelled the end dates on thousands of service members’ contracts, forcing them to stay on active duty. If there had been no G.I. Bill to attract the flow of new recruits in that period that it did, what would the military have been forced to do to swell its ranks?

Making college more affordable and accessible is necessary. However, there are no clear solutions to fixing what could be the undermining of the G.I. Bill and exacerbating the costs of sustaining a volunteer force. Perhaps the government could reallocate the funds it would have spent on tuition payments to pay a larger percentage of veterans’ living costs while in school. But if college is free, will doubling the living expenses allowance to $4,000 a month persuade sufficient numbers of the right people to sign their lives over for four years? Or would simply higher pay be sufficient? If it were, it would have to be substantially higher than current pay levels, likely compounding objections regarding the government budget deficit and defense spending in general.

Some may argue that access to higher education is more important than the military’s ability to recruit. While that may be true, government’s traditional primary function has been national defense. It is national defense that ultimately enables all people — whether or not they have ever served in the military — to pursue higher education in peace and security. Nor does service preclude people from pursuing higher education. It simply delays it, while also equipping veterans with valuable life skills.

Other critics may say that linking free college to military service amounts to coercion and is inherently unequal. To address the issue of inequity while also remaining effective, the only remaining stopgap option may be the least politically palatable of all: the reinstitution of the draft.

No serious stakeholders want a return of the draft. Military leaders prefer the reliability and precision of the professional force over conscription. Similarly, few civilians — parents or young people — want compulsory service. But as the government universalizes healthcare and, now possibly, higher education, it may tie its own hands, requiring the re-imposition of involuntary military service.

With women now permitted to serve in the combat arms specialties of the military, Congress is considering having them register for the draft at 18 just as men have long been required to do. If that should happen, our first female commander-in-chief may also be the first to oversee a draft of women into uniform.

If Clinton is elected, she should take these concerns seriously and revise her current free college proposal accordingly. It is important to mitigate the negative impacts of any major education access programs on military recruiting and find new, affordable ways to ensure the military can continue to meet its manpower requirements under a range of national security scenarios.

Benjamin Luxenberg, a Marine Corps veteran, is enrolled in the joint MBA/MPP program of Harvard Business School and the Harvard Kennedy School of Government. He is an Associate Scholar of the Foreign Policy Research Institute.

Image: U.S. Air Force photo by Master Sgt. Bill Wiseman