The concept of representational contamination is introduced to account for psychological changes in the public sphere after a local armed clash deflects a national peace process. Although representational contamination is fundamentally psychological, our conceptualization of this phenomenon merges ideas from other social science disciplines such as media communication, political derailment, and intergroup conflict. We push psychology to more macro layers of analyses, and increase its theoretical utility for social issues such as peace and conflict. As a case in point, we take the Muslim-Christian peace process in the Philippines, as positive representations of the Bangsamoro Basic Law (BBL) shift dramatically and negatively after an armed clash in the remote municipality of Mamasapano. Our research innovates a methodological mix of qualitative and quantitative strategies to access natural data in the real world, obtain mathematical accuracy, and add discursive depth. We employ a sequential mixed methods strategy on a data corpus of 178 news reports about the BBL, 5 weeks before and 5 weeks after the Mamasapano clash. Text-mining calculations yield word association scores of support (range 57%–89%) and confidence (consistently 100%), indicating a high discursive overlap between BBL and Mamasapano. Computed word association maps also show how BBL is associated with positive words before Mamasapano and negative words after the military encounter. We end by raising practical questions on how to deal with representational contamination, and discuss issues of psychological containment in the public sphere.