In this NVivo 12 textual analysis package files and Stata 17 datasets, the focus is on the arguments presented by 40 leading analysts of European security in their arguments for their view on whether NATO enlargement was a mistake. The selection of the experts was done by the Foreign Affairs journal that published an opinion survey of 62 experts of which 40 published their arguments in addition to their opinions in this survey publication of Foreign Affairs (Foreign Affairs Survey 2022). These arguments by 40 of the 62 surveyed experts is the textual material of this dataset. The textual data was coded to reveal premises of these experts. The coding was based on distinctions that the creator of this dataset created on the basis of literature reviewed in his article “Theoretical Premises of Support of and Opposition to NATO Enlargement.”