As the US increasingly withdraws from multilateral institutions it had set-up and maintained with its European partners, EU actors are confronted with a steep trade-off: Should they step up their commitment to defend multilateralism; or should they follow geopolitical imperatives, continue business as usual or even follow the US disengagement? This paper starts out to examine how EU actors cope with this trade-off and argues that European engagement is conditioned by EU actors’ trust in affected IOs’ bureaucratic leadership. When EU actors trust in the bureaucratic leadership of an IO abandoned by the US, they will bear the addition costs of stepping up support for the organization. When EU actors distrust the IO bureaucracy, they will refrain from additional support or even disengage from the organization themselves. The paper assesses this trust hypothesis empirically by studying the EU’s varying support for two UN development institutions the US withdrew from under the first Trump Administration: the United Nations Population Fund (UNFPA) and the United Nations Relief and Works Agency for Palestine Refugees in the Near East (UNRWA). An in-depth analysis, leveraging interviews with EU and IO officials, corroborates the expectation that EU actors’ support for multilateralism is selective. This has important implications for the rules-based order and the EU’s role within it.