How did the signing statements of the modern presidency before Watergate shape the development of the tool and contribute to its institutionalization? A content analysis of the 626 signing statements from 1933 to 1974 shows that the Eisenhower, Johnson, and Nixon administrations set important precedents for the modern constitutional use of the tool by protecting the institution from legislative vetoes and perceived encroachments in regard to foreign affairs and executive privilege. The results reveal that the constitutional logic required for the growth of challenges is rooted in this era and that Watergate served to amplify a trend that was already in motion.