How US midterms could affect Trump's tariffs, defence spending and foreign policy

The US midterm elections on November 3 will determine which party controls Congress, shaping President Donald Trump's ability to pass legislation, approve budgets and implement his agenda during the final two years of his presidency. The results could also influence US policies on trade, immigration, defence spending and conflicts abroad, particularly the war with Iran. Unlike presidential elections, midterms do not determine who occupies the White House. Instead, voters elect members of Congress, comprising the House of Representatives and the Senate. The outcome will decide whether Republicans retain control of both chambers or Democrats gain the power to challenge Trump's agenda. How would the results affect Trump's legislative agenda? Congress passes laws, approves federal spending and oversees the executive branch. Control of either chamber can determine which proposals advance and which are blocked. Republican majorities have helped Trump secure key priorities, including increased funding for immigration enforcement and major tax and spending changes under the 2025 tax law. However, disagreements have emerged within the party over tariffs and congressional authority concerning the war with Iran. If Democrats win control of the House, they could challenge Trump's policies on healthcare, immigration and trade, while launching investigations into his administration and family business interests. They could also initiate impeachment proceedings. Even if Democrats control both chambers, passing their own legislative agenda would remain difficult. Trump retains the power to veto bills, and overriding a veto requires a two-thirds majority in both the House and Senate. A Democratic victory would therefore be more likely to constrain his agenda than replace it entirely. Why could the midterms become a test of foreign policy? Foreign policy rarely ranks among the top concerns of American voters, who typically prioritise inflation, jobs and household expenses. However, the economic consequences of decisions taken abroad could make it more influential this year. The 2026 Chicago Council Survey, conducted from July 10 to 21, found that 37% of Americans identified inflation and the cost of living as the most important issues influencing their vote. Only 2% named the war with Iran as their top concern. Yet 86% said the conflict had harmed the US cost of living, while 81% said tariffs had done the same. These findings suggest voters may judge foreign policy through its impact on fuel prices, consumer costs and household finances. Rising energy prices could hurt Republican candidates in competitive races, even when foreign affairs are not voters' primary concern. Trump's handling of Iran and his trade policies could therefore become electoral liabilities, potentially limiting his room to pursue military action or negotiate with foreign governments. What could change in trade, budgets and defence spending? A Democratic-controlled chamber could increase scrutiny of Trump's tariff programme and push for changes to trade policy. However, gaining control of Congress would not automatically allow Democrats to reverse every presidential decision. Federal spending could become another flashpoint. Congress must approve funding legislation, and divided control could make budget negotiations more difficult, raising the risk of temporary funding extensions or a government shutdown. Defence spending and overseas military commitments could also face closer scrutiny. Lawmakers may seek to assert Congress's role in decisions concerning the war with Iran, while debates over military aid and the cost of foreign engagements intensify. Markets will also watch the results for signals on government borrowing, budget deficits and spending. A change in congressional control could complicate Trump's economic agenda, although neither party has offered an obvious solution to the country's longer-term fiscal challenges. Could a Democratic victory lead to Trump's impeachment? Trump has warned that Democrats could seek to impeach him if they win control of Congress. He was impeached twice during his first term. A Democratic majority in the House would give the party control of key committees, allowing lawmakers to launch investigations, issue subpoenas and vote on articles of impeachment. However, impeachment alone would not remove Trump from office. Conviction and removal require a two-thirds majority in the Senate. A Democratic victory would therefore mean greater scrutiny of the administration and more obstacles to Trump's legislative plans, rather than automatic removal from office. What happens if Republicans retain control? If Republicans retain both chambers, Trump would be better positioned to pursue his domestic agenda, confirm nominees and negotiate spending priorities. However, narrow majorities would not guarantee party unity, particularly as lawmakers begin positioning themselves for the 2028 presidential election. The election could also shape US foreign policy. An electoral setback might encourage Trump to adopt a more restrained approach, but it could also prompt him to double down on controversial policies. Ultimately, the midterms will determine how much Congress can enable or constrain Trump over the next two years. Their wider impact will depend not only on which party wins, but also on how lawmakers respond to voters' concerns about the economy, military conflicts and America's role in the world.