Mosse's first academic appointment as an historian was at the University of Iowa, where he focused on religion in early modern Europe and published a concise study of the Reformation that became a widely used textbook. Here he organised opposition to McCarthyism and, in 1948, support for the Progressive Party presidential campaign of Henry A. Wallace. Despite being in the center of a conservative farm state, he experienced no personal repercussions. Against Jospeh McCarthy he found allies among conservative Republicans who regarded the red-baiting senator as a "disruptive radical".