In understanding the willingness of government lawyers to defend the constitutionality of federal statutes, this article will explain why presidents rarely make use of their powers under the Constitution (allowing the president to refuse to defend laws he finds unconstitutional) and under federal law (placing the control of most government litigation with the attorney general). Attention will be paid both to how Department of Justice lawyers enhance their power by defending federal statutes and to how Congress, if need be, can pressure the department to bow to lawmaker preferences. In consequence, when the president refuses to defend a statute, courts have little reason to disregard article III constraints to resolve constitutional challenges to federal laws.