This essay responds to the claim that presidential rhetoric has little effect. It addresses three questions: (1) How do we understand the nature of presidential rhetoric and its effects? (2) What does presidential rhetoric do? (3) How do we know? From the perspective of the humanities, rhetoric is a complex transaction among speakers or writers, audiences, and critics. Effects are better understood as invitations to respond. A key function of presidential rhetoric is to define social reality, and this power to define is a significant presidential resource. Eight case studies explore how presidents from George Washington to George W. Bush have relied on rhetorical definition. This essay originally was presented at a research symposium at Texas A&M University. It is reprinted here from Presidential Studies Quarterly, 34 (September 2004), 607–619.