Since the beginning of his second term, U.S. President Donald Trump has taken a contradictory approach to the war in Ukraine and how it should end. In September 2025, Trump said that Ukrainians should “get their land back” and that Russia was “a paper tiger.” Just two months later, however, he presented a 28-point peace plan widely seen as favorable to Russia, saying that Ukraine would “lose in a short period of time” if it did not agree to the plan. Since then, Trump has continued his efforts to end the war as quickly as possible, even if that path results in a bad deal for Ukraine. Such an approach is insufficient to ensure that Ukraine can maintain its sovereignty and remain intact.

But Ukraine’s survival is not up to Trump alone. Congress has the tools to shape U.S. policy toward Kyiv regardless of the president’s position. It also has historical models for action: the Taiwan Relations Act and the bill to lift the Bosnian arms embargo. In 1979, after President Jimmy Carter withdrew diplomatic recognition of Taipei in favor of Beijing, Congress intervened to preserve U.S. links to the island. Through the Taiwan Relations Act, Congress used its authority to regulate U.S. commerce, cooperate on security measures, and sell arms for defensive purposes, ensuring that Washington and Taipei maintained relations, albeit informally. The act committed the United States to a position of strategic ambiguity that required it to maintain the ability to defend Taiwan militarily but without definitively committing U.S. forces. This legislative commitment to Taiwan enabled Congress to constrain the executive’s policymaking flexibility without trespassing on its diplomatic authority.

Nearly 15 years later, in July 1995, Congress acted again to shape the president’s foreign policy, voting to lift an arms embargo on Bosnia and Herzegovina. President Bill Clinton had supported the embargo as a means to limit violence in the country’s civil war, whereas Congress saw it as limiting Bosnian Muslims’ ability to protect themselves from violence by Bosnian Serbs. Although Clinton vetoed the bill, its passage sent a message to the president that Congress was watching. Just two weeks later, the president backed a NATO bombing campaign targeting Bosnian Serb positions.

Congress can apply these models of action to Ukraine by advancing a bipartisan “Ukraine Relations Act” that affirms U.S. support for Ukraine’s territorial integrity and provides strong security guarantees against future Russian aggression. It would maximize the power and influence Congress has over foreign policy by shaping the conditions under which territorial disputes are negotiated and enforced. When it comes to ending the war, the passage of such an act would strengthen Ukraine’s position in negotiations and make it harder for Trump to unilaterally force Kyiv to........

© Foreign Affairs