This essay illuminates the role of emotion in antebellum American politics and political culture through an analysis of the indignant northern response to the May 1856 caning of Charles Sumner. It begins by situating indignation in its antebellum cultural context, showing that popular beliefs about indignation's sympathetic and moral nature made it a uniquely respectable and highly valued type of anger. Indignation enjoyed additional political power when expressed collectively in a so-called "indignation meeting," a staple of antebellum American politics. This political ritual brought like-minded citizens together to respond to public problems and to influence elected officials. Scores of the meetings convened throughout the free states following the Sumner assault. As they met to express their shared indignation against Sumner's assailant and to demand retaliation against the southern slave power, many northerners experienced an intense feeling of sectional unity which appeared to bridge partisan and ideological divisions. This perceived unity, coupled with widespread belief in the need for northern unity against southern aggression, decisively aided the rise of he Republican Party. By appealing rhetorically to northern indignation, and by holding their own partisan indignation meetings, the Republicans harnessed northern indignation to their cause, an opportunity missed by their political rivals.