U.S. college enrollments have declined by 3 million students over the past decade. While the decrease has been concentrated in community colleges, it’s coming soon to many four-year institutions. Demographers predict an “enrollment cliff” beginning in 2025, when the traditional college-age population will start shrinking for the foreseeable future. Unless they bring in more students, colleges will struggle financially, and some could shut their doors. Some are already doing so.