The purpose of this article is to analyze the United States’ support to Ukraine during the war with Russia, as well as in the months leading up to Russia’s full-scale invasion of Ukraine in February 2022. This issue remains relevant to conceptualizing US assistance to Ukraine to expel Russian forces from its territory. In particular, we claim that among other policy alternatives, the Biden administration deliberately chose to support Ukraine «for as long as it takes». Thus, we analyze the amount and comprehensiveness of support to Ukraine, which we consider to be in Washington’s core interests, as well as US efforts in terms of policy-making. The methodological design of the study is based on discourse analysis as a major method, which allowed us to examine the policy choice of the Biden administration to provide massive and comprehensive support to Ukraine in a critical time of need. When describing US assistance, we apply historical institutionalism and rational choice institutionalism as the major theoretical paradigms, as there are features of both used by the United States in its bilateral relations with Ukraine. We operate within a confirmatory research design, where the major method is hypothesis testing. The scientific novelty consists of an attempt to conceptualize the so-called Biden doctrine in the context of American assistance to Ukraine in order to sustain it in the war against Russia. We test our hypothesis on three major dimensions: the President’s authority, Congress and the U.S. leadership of NATO, and the Defense Contact Group. The authors conclude that the amount of US support to Ukraine and its comprehensiveness, particularly economic and military aid, indicate that the Biden administration viewed Ukraine as a test of its vision of foreign policy, namely that democracies should prevail over autocracies. Therefore, the unprecedented amount of aid allocated to Ukraine suggests that the support will last as long as it takes.