The conventional story of American Catholics and religious freedom on the eve of the Second Vatican Council (1962-1965) is fairly straightforward. Before Vatican II, US Catholics were largely embarrassed by Rome's principled opposition to religious and other liberal freedoms. They rallied behind their foremost theologian, John Courtney Murray (1904-1967), to push for change in Roman Catholic church-state doctrine. After silencing Murray for nearly a decade, Vatican authorities, at last, recognized the value of disestablishment, and the Council finally reconciled Catholicism to American democratic liberties. Through qualitative research in nine different archives in both the United States and Rome—including newly available Vatican documents from the time of Pius XII's pontificate—the present dissertation complicates this narrative by foregrounding the position of the American Catholic hierarchy, eager to remain in good standing with Rome even while operating within a religious freedom regime. To do so, they imported arguments rooted in the Roman anti-liberal tradition to the broader Americanconversation on the place of religion in democracy—a debate that was intensifying between the late 1930s and the early 1960s. The bishops argued that the US regime of religious freedom in fact made America not a "secular," but a "covenant nation"—a confessionally ecumenical covenant for sure, but a covenant, nonetheless, which welcomed the Church onto the public square. The bishops supported the "Nation Under God" campaigns of the 1940s and 1950s and joined non-Catholics who shared their aversion to the "naked public square" to defend their church-state vision in the courts. Meanwhile, Rome learned to appreciate disestablishment, if not for its intrinsic virtues (the John Courtney Murray argument), at least because it did not necessarily preclude the possibility of close church-state cooperation in an increasingly secular world. In the short run, this vision ultimately clashed against the Warren Court's embrace of stricter church-state separation standards, while Rome finally let Murray help reframe Catholic doctrine on religious freedom at Vatican II. But even now, the Nation Under God project preserves its appeal to new cohorts of liberalism's discontents.