Much of the conventional wisdom about partisan media effects is based on the single case of the United States. Without more comparative research, we know little about whether the findings are generalizable, however, and thus cannot be certain of their causes. But comparative research presents several challenges. This paper takes advantage of the case of the War on Iraq to examine the effects of partisan press coverage on perceptions of leaders and ultimately on voting behavior in two countries, the United States and Britain. We test three competing hypotheses of partisan media effects. We find support for the argument that the reputation of the incumbent party moderates the influence of partisan coverage on perceptions of war but also show that opposition partisan media coverage undermines perceptions of the qualities of incumbent leaders. Media outlets that support the incumbent do not have similar positive effects. We conclude that the war cost a left-wing leader, Blair, more than a right-wing leader, Bush, because of (1) the ambivalence of incumbent-supporting newspapers in Britain, (2) the absence of a parallel to the boost in approval that incumbent-supporting newspapers provided for Bush, and (3) greater damage to perceptions of Blair’s attributes among readers of opposition-supporting newspapers.