<Online Only>This chapter examines the unsettling of the political constitution by domestic challenges to the euro crisis response, particularly against the actions of the European Central Bank (ECB). The disconnect between postnational discourse and domestic constitutionalism generated critical constitutional moments over who was ‘the guardian’ of the European constitution. These moments were exemplified by the OMT saga, when the German Constitutional Court threatened to invalidate an ECB programme that had existential implications for the eurozone. The chapter will examine how the ECJ’s assertive ruling, in response, did not signal the perfection of European constitutionalism, as suggested by the new constitutionalists, but revealed its precarity, rubber-stamping a programme that was of dubious legitimacy. If this would ‘buy time’ for the project, it would do so in a way that merely concealed the dysfunctionality of Economic and Monetary Union. The chapter concludes that authoritarian liberalism was, ultimately, juridically fortified by these challenges, but left open to further constitutional contestation, revealing the erosion of sovereignty underlying the European construct.</Online Only>