Scholars and laypeople have become concerned that American religion and politics has increasingly divided between conservatives and liberals, resulting in a "culture war" that leaves little common ground on salient social issues. Drawing on archival and periodical sources and a comparative-historical research design, I seek to understand the causes and consequences of the shifting relationship between religion and politics by examining how large, moderate and mainstream Protestant institutions have struggled to maintain cohesion and prestige throughout the increasingly contentious politics of abortion. In the early-1960s, no Mainline Protestant institutions supported expanding abortion access. Over 1966-1972, all the same institutions released official pronouncements in support of expanding abortion access. Since this time, particularly from 1987-1992, all these institutions faced increased internal debate over the issue and shifted in conservative directions to varying degrees. I find that the debate around abortion among Mainline Protestant institutions was not generally characterized by polarization around two sides but rather by much consensus, change over time, ambiguity, and often ambivalence toward the issue. These stances have often emerged not out of existing worldview and attitudes, but rather out of existing social networks, awareness of stances by others in the religious field, and institutional self-interest. Protestant clergy who put in significant time, energy and personal risk into expanding abortion access for women in the late-1960s and early-1970s were pulled into the movement through existing activist social networks, particularly from the Civil Rights Movement, and attitudes towards other issues such as civil rights, social injustice, and civil disobedience. During the 1960s and 1970s, Mainline Protestant institutions mobilized around support for expanding abortion rights as a way of challenging the political power of Catholic institutions, which were the primary opponent to expanding abortion access. Over the 1980s, as Evangelical Protestants became increasingly engaged in pro-life politics, Mainline Protestants began to see them as the primary opponent to expanding abortion access. Those denominations that sought to create greater ties with Evangelical Protestants backed away from their support of choice, while those denominations that sought to distinguish themselves from Evangelicals remained support of choice despite strong pro-life grassroots movements within them.