Now, as a new academic year begins, American dominance in higher education globally is incontrovertibly in decline, according to data, international rankings and independent experts. The slide has been accelerated by a year and a half of funding cuts, restrictions on international students and curbs on what can be said or taught. But it began before those political challenges, with enrollment declines, lackluster returns on ever-rising prices and public mistrust. “It takes a while for all of these problems to trickle down, but they are beginning to trickle down,” said Eric Mlyn, a faculty fellow at the Kenan Institute for Ethics at Duke University who studies academic freedom.