The liberal international order (LIO) is experiencing a legitimacy crisis in its Western heartland. What causes this crisis? Existing approaches focus on the LIO’s unequal allocation of wealth and values that produces losers and thus breeds dissatisfaction. Yet, why this dissatisfaction translates into a delegitimation of the order rather than a contestation over policies remains unaccounted for. Complementing the cultural and economic backlash hypotheses, this paper advances an institutionalist explanation for the current crisis of the LIO, which accounts for the growing resistance to the LIO with a political backlash hypothesis. Our argument is that the institutional characteristics of the LIO’s political order trigger self-undermining processes by inciting opposition that cannot be politically accommodated and is thus bound to turn into polity contestation. In particular, we hold that IOs’ predominantly technocratic legitimation rationale on the one hand, and their increasing political authority with distributional effects on the other, create a democracy gap. It implies that avenues to absorb opposition through input channels are largely missing and thus incite the erosion of the LIO’s general acceptance. We illustrate the plausibility of this argument with evidence from the European Union (EU) as well as the international regimes on trade and human rights.