Patty Spillman and Jen Belt drive through the outskirts of Grove City, Ohio, mapping the battle lines of a war they’ve waged for months. Pointing out the window of Belt’s blue Chrysler mini-van, Spillman notes the precise borders of a proposed 310-acre data-center campus. She singles out the electrical substation and towering power lines, and recounts the personal histories of neighbors who got offers to sell their land to Headwaters Site Development, the Texas-based company proposing to construct a cloud-computing storage facility on this patch of rural farmland about 10 miles outside Columbus. In between fields of drying corn-stalks and short rows of soybeans, some farmers have planted “ no data center ” signs on their lawns.

Spillman’s 165-year-old farm sits across the street from the proposed complex. A soft-spoken retired bus driver, Spillman, 63, is a Republican who voted for President Donald Trump three times. Belt, a 51-year-old artist and marketing contractor, is a Democrat.…