Scholars and jurists have long assumed that, when the executive branch declines to defend a federal statute, Congress may intervene in federal court to defend the law. When invalidating the Defense of Marriage Act, for example, no Supreme Court Justice challenged the authority of the House of Representatives to defend federal laws in at least some circumstances. At the same time, in recent litigation over the Fast and Furious gun-running case, the Department of Justice asserted that the House could not go to court to enforce a subpoena against the executive. In this Article, we seek to challenge both claims. We argue that Congress has the constitutional power to enforce subpoenas but not defend federal statutes in court. Congressional defense of federal statutes violates two constitutional norms. First, except in certain specified situations (none of which are applicable here), the Constitution prohibits Congress or one of its components from having any role in the implementation of federal law. Second, unilateral defense by the House or the Senate violates the constitutional norm of bicameralism. The Constitution does not authorize either chamber to speak on behalf of Congress, much less the United States, in defense of federal law. By contrast, the Constitution gives each chamber considerable power to investigate wrongdoing by the executive and to conduct litigation growing out of such investigations—by, for example, enforcing subpoenas. We believe that this limited congressional power to appear in court makes eminent sense. The House and Senate counsel, as currently constituted, are poorly suited to defend their joint work product in court but are well situated to represent their respective institutions in other proceedings against the executive. Furthermore, this investigative power gives each chamber a powerful (and often overlooked) constitutional tool to do battle with the executive.