Theoretical understandings of the backlash against international investment law and arbitration can benefit from examining analogous dynamics in supranational governance more generally. Two features characterize both systems: the delegation of regulatory power to functional pre-commitment agents beyond the State; and the persistence of constitutional legitimacy in State-level principals. In these circumstances, the ‘agency-cost problem’ is aggravated in two ways that find surprising support in the literature. Global administrative law, for example, comes close to rationalizing a system of ‘agents without principals’ by bracketing whether any legitimating connection between the two is possible. Pluralist-constitutional theorists, by contrast, cast pre-commitment agents as representatives of a global constitutional order, thus rationalizing a ‘principal-agent inversion’. Either way, a break occurs in the ‘power-legitimacy nexus’ thus leading to backlash.