In this article, a theoretically informed and historically grounded perspective on ideology and ideologues is developed to address a paradox: while presidents play a central role in articulating socially diffuse ideologies, such as the soft-Statism of the New Deal or the anti-Statism championed by today's Republican Party, few administrations have been hospitable to ideologues, the True Believers who develop ideologies in the first place and are dedicated to their implementation. While institutional inducements to the presidential employment of ideologues have grown throughout the modern presidential era, differential inducements to their influence have been critical in explaining when, and how, both ideologues and ideology have intersected with the modern presidency. These differential inducements are exogenous crises, the regime characteristics of each presidency, and the personal traits of presidents. The interplay of these factors is charted from Franklin Delano Roosevelt (or FDR) through the Obama administration.