ABSTRACTThe suitable personality traits for optimal leadership may depend on the type of leadership, the criterion of leader effectiveness, and various situational constraints This point was illustrated via the specific area of presidential leadership The working relationship between the Chief Executive and Congress, as defined by regular vetoes and vetoes overturned, provided the criterion variables for a congressional time‐series analysis (N= 99) of all 39 American presidents The impact of a single personality attribute, presidential inflexibility, was examined in the context of several variables suggested by past research The relation between inflexibility and willingness to exploit the regular veto varied according to the incumbent's electoral mandate, while the association between inflexibility and the propensity of Congress to override a veto depended on the extent to which the president's party controlled Congress—this last interaction was labeled the Johnson‐Wilson effect In the context of the person‐situation debate, these findings illustrate how certain situations can determine whether, and to what degree, a stable individual attribute will have behavioral manife