Democratic Gains in Congress Could Constrain Donald Trump’s Foreign Policy

Democrats’ victory in the U.S. midterm elections is expected to create new obstacles for President Donald Trump’s foreign policy. With control of both the House of Representatives and the Senate, beginning in January 2027, Democrats will have tools to scrutinize White House decisions, question military operations and influence funding for conflicts. Trump will remain responsible for foreign policy and command of the armed forces, but he will face an opposition-controlled Congress less inclined to support his administration.

Potential flashpoints include the war with Iran, U.S. military aid to Israel and Ukraine, and pressure on countries in Latin America. The scope of the change will depend on how willing Democrats are to use their congressional powers. A new majority could make parts of Trump’s international agenda harder to carry out, but it cannot automatically replace decisions made by the executive branch. Leo Braga, an international relations professor at Faculdade Presbiteriana Mackenzie Rio, said the main shift would be a greater need for negotiation between the branches of government. “That does not mean Democrats will have a much easier time with this,” he said.

Discontent over the cost of living, inflation and rising fuel prices combined with opposition to immigration operations and U.S. involvement in international conflicts. The war with Iran, in particular, brought together voters’ concerns about the economic cost of presidential decisions and the administration’s priorities. Fernanda Brandão, an international relations professor at Faculdade Presbiteriana Mackenzie Rio, said Democratic gains were driven mainly by opposition to the Republican administration and the effects of its policies on daily life. She said the “blue wave” was largely explained by rejection of the Trump administration and the negative impact of its policies on Americans’ cost of living.

The military offensive against Iran, which began in February 2026, has had economic and political effects in the United States, including higher fuel prices and increased public spending. The conflict also became one source of electoral damage for Republicans. With majorities in both chambers, Democrats can question whether operations should continue, call officials to testify and seek greater transparency about the administration’s military objectives and costs. Congress also approves the federal budget and can place conditions on defense funding, potentially making it harder to sustain an operation lawmakers oppose. Braga said limits on the defense budget could leave the government without money to produce missiles, deploy troops or refuel naval vessels.

Fernanda Medeiros, an international relations professor at the University Center of Brasília (CEUB), also identified the budget as a key way for the opposition to exert pressure. Foreign policy is an executive responsibility, she said, but Congress can and should monitor the administration and demand answers. She expects a shift from a Congress that endorses White House actions to one more willing to investigate major issues, including tariffs, political interference in other countries and the war with Iran.

Democrats are also expected to scrutinize military assistance to Israel, one of the main recipients of U.S. aid. Continued funding could face questions from lawmakers who criticize what they view as unconditional support for the government of Prime Minister Benjamin Netanyahu. Trump has said he intends to cut funding to the Israeli government. On Ukraine, Democratic gains could increase pressure on Trump to maintain military and financial aid to Kyiv and sanctions against Moscow. Since the start of his second term, Trump has reduced U.S. involvement in the war and pressed Volodymyr Zelensky to consider territorial concessions to Russia. Braga said a Democratic-controlled Congress could improve Kyiv’s negotiating position by making it harder to reduce funding for Ukraine’s defense; he expects the slow flow of U.S. budget support to ease.

In Latin America, congressional oversight could extend to U.S. sanctions, diplomatic pressure and security operations. Secretary of State Marco Rubio, a leading figure in Washington’s policy toward the region, could face more frequent questions from lawmakers. Medeiros said the region may feel the effects of the change, particularly through investigations into Trump administration decisions. She noted that a group of Democratic lawmakers had already sought explanations from the U.S. government over possible interference in Brazil’s elections. No immediate change in U.S.-Brazil relations is expected, but Braga said the election result could strengthen Brasília’s diplomatic leverage as Trump faces a more powerful opposition. He also argued that Lula’s continuation in office for four more years could weaken Trump, who would have only two years left in his term starting in 2027, and alter the countries’ bilateral dynamic.