Did Franklin Delano Roosevelt escalate confliict with Japan and Germany before Pearl Harbor, or did he attempt to avoid war? To what extent did U.S. public opinion influence these decisions? And, crucially, how do we know? Scholars offer diametrically opposed analyses of this historical case, bearing directly on international relations theories regarding the effects of democracy on war and foreign policy. In this debate and the broader security studies field, scholars increasingly employ published and archival primary sources. Because researchers lack a clear template for descriptive and causal inference with documentary evidence, though, such work is indeterminate and ultimately unpersuasive. How can political scientists approach archives and primary documents more effectively and efficiently? Above all, case studies need stronger research designs and clearer source selection strategies, not just more authoritative documents. A critical review of the sources cited in recent scholarship in the debate leading to the United States' entry into World War II, and a replication analysis of a key portion of the documentary record, underscores this need for improved research design and buttresses eight guidelines for the selection and analysis of textual evidence in case study research.