This chapter delves into US relations with the governments of Afghanistan and Iraq in the post-9/11 era. The chapter describes the idiosyncratic processes that led Afghanistan to have presidential institutions and Iraq to have parliamentary institutions. It then shows how the different constitutional arrangements in Afghanistan and Iraq changed the dynamics through which the United States interacted with incumbent leaders, and their potential successors, in the two countries. It analyzes the extent to which the United States was able to exercise leverage over the incumbent leaders in Afghanistan and Iraq, respectively, given their different constitutional frameworks.