The article is dedicated to the analysis of “strategic ambiguity” concept – a tool of U.S. foreign policy aimed at dual deterrence of both mainland China and breakaway Taiwan. Washington stayed deliberately ambiguous in its commitments to defend Taiwan thus leaving Beijing uncertain whether the U.S. will intervene in case of escalation in the Strait, and at the same time not encouraging Taiwanese authorities to declare full independence and sovereignty which would provoke military escalation with mainland China, dragging the U.S. into full-scale conflict with the Chinese People’s Liberation Army (PLA). The article analyzes the roots of this approach during D. Eisenhower’s years in office, its evolution en course and after the Cold War, and its erosion under D. Trump and J. Biden. The article shows that the U. S. President Eisenhower wished to maintain status-quo in Taiwan Strait, fearing that he would either have to turn a blind eye on the communist takeover of Taiwan, or be dragged into conflict with the close ally of Moscow, which would eventually lead to the war with the USSR. Eisenhower and his administration remained ambiguous in their communications with the PRC (mainland China) and Taiwan, not encouraging the island to declare full independence and at the same time not giving Beijing a carte blanche for military intervention. This approach dubbed in political science and international relations theory as “strategic ambiguity” proved to be useful, and was reinforced during Washington–Beijing rapprochement in 1970s. Under Trump administration, the U.S. started to consider dropping the “strategic ambiguity” policy towards clearer deterrence commitments. This trend manifested via emotional statements made by Donald Trump himself, mostly on social media, as well as through a change of tone in key foreign policy documents and new decisions that signaled a serious revision of the American approach to military cooperation between the United States and Taiwan. This trend continued and exacerbated under Biden administration due to number of bills signed, including the Taiwan Enhanced Resilience Act (TERA) which de-facto dubbed the contested island as Washington’s “Major Non-NATO Ally” and enabled to boost military supplies. The erosion of the “strategic ambiguity” policy also manifested through various high-profile contacts, including the House Speaker Nancy Pelosi’s visit on the island.