Abstract: Ruth Wodak's Discourse-Historical Approach (DHA) focuses on political fields, emphasizes political discourses' social-historical context, and traces the diachronic change of discursive events.Starting from strategies of nomination, predication and perspectivization in DHA and combining corpus techniques, the research, through analyzing keywords and concordance lines, reveals that news reports about Clinton email in American mainstream media during the 2016 US presidential campaign affect attitude change from negative to positive, and that discursive constructions of this event go through a diachronic change from out-group to in-group.This transformation is mainly embodied in different discursive strategies employed by the media to meet different needs at different stages, highlighting media's political stance and ideology endorsing political elites.The study shows that combining DHA and corpus techniques is an effective tool for analyzing ideology in political discourse.