US midterm results: How a Democratic Congress could constrain Trump on Iran war, Ukraine policy

US President Donald Trump is set to face a significantly tougher political landscape after the Democratic Party secured control of both chambers of Congress in the November 3, 2026, midterm elections.

The sweeping electoral setback for Republicans will reshape the balance of power in Washington.

The changes in the US Congress are likely to complicate Trump's foreign policy agenda during the final two years of his presidency.

Quick answers to key questions

•4

QUESTIONS

Democrats could investigate administration decisions, summon officials to hearings, scrutinise military operations and defence spending, and challenge policies through legislation. Trump would still retain substantial authority over diplomacy and military operations.

The war and its effects on fuel prices, inflation and the cost of living were major election issues. Those domestic concerns could increase pressure on the administration to change its approach or seek an exit.

Congress could use its influence over legislation and spending to challenge war-related policies, but completely blocking the spending could be difficult. Trump could veto legislation, and lawmakers would need a two-thirds majority in both chambers to override a veto.

Democratic lawmakers could scrutinise Trump's approach, including any pressure on Kyiv to accept terms favourable to Moscow. A weaker Republican position in Congress could also make it harder for Trump to secure political backing for a policy seen as too accommodating to Moscow.

The Democratic victories in the House of Representatives and the Senate give the party greater leverage to challenge the administration through congressional investigations, legislative action and scrutiny of federal spending.

The outcome comes at a critical time for the Trump administration, particularly as the US remains embroiled in the conflict with Iran, which began with joint US-Israeli strikes on February 28.

The war, along with rising fuel prices, inflation and the broader cost-of-living crisis, emerged as a major issue during the election campaign.

While Trump retains considerable executive authority over diplomacy and military operations, a Democratic-controlled Congress could make it harder for him to pursue his foreign policy objectives, as he would face political and legislative resistance.

How Democrats' Congress takeover could constrain Trump

Democratic control of both chambers will give the party greater power to investigate the administration's decisions, summon officials for congressional hearings, and demand explanations for contentious policy choices.

This could put several aspects of Trump's foreign policy under closer scrutiny, including the legal basis, financial costs and conduct of the war with Iran.

Laurel Rapp, director of Chatham House's US and North America Programme, told CNBC that Trump would face greater constraints on oversight and investigations, although his authority over foreign policy would remain substantial.

"We are going to see a president that is somewhat constrained on matters of oversight and investigation, but on foreign policy, he does still retain a lot of latitude," Rapp told CNBC.

The Democratic majority could also use its legislative influence to challenge Trump's broader policy agenda.

Iran war: Will Trump face pressure to find an exit?

The conflict with Iran is likely to become one of the biggest foreign policy flashpoints between the White House and the new Congress.

Rising fuel prices, food costs and inflation linked to the conflict have added to public dissatisfaction with the administration.

The economic fallout also made the Iran war a significant issue in the midterm election campaign.

Rapp described the conflict as a "major issue" in the election cycle, suggesting that its domestic economic consequences could intensify pressure on the administration.

However, completely blocking the administration's war-related spending could be difficult, as per the expert.

Any legislation passed by Congress would still face the possibility of a presidential veto, which lawmakers would need a two-thirds majority in both chambers to override.

Ukraine war: Could Trump's approach towards Kyiv face resistance?

The Russia-Ukraine war could become another major source of friction between the White House and Congress.

Trump's approach to the conflict, particularly his willingness to pressure Kyiv into accepting terms favourable to Moscow, could face greater scrutiny from Democratic lawmakers and even members of his own Republican Party, as per experts cited by CNBC.

According to an expert cited by CNBC, the Ukraine conflict represents a potential "tail risk", with concerns that Trump could seek to pressure Ukraine into effectively surrendering to Russian demands.

Several Republicans, including Secretary of State Marco Rubio, do not share Trump's apparent sympathy towards Russian President Vladimir Putin, potentially creating further divisions within the administration's political support base.

A weakened Republican position in Congress could therefore make it more difficult for Trump to secure political backing for a Ukraine policy that is seen as too accommodating towards Moscow.

What the election means for US foreign policy

The Democratic takeover does not automatically transfer control of US foreign policy to Congress.

The president retains considerable constitutional authority over diplomacy, military command and negotiations with foreign governments.

However, the new congressional arithmetic could change the political calculations surrounding Trump's decisions.

Investigations into military operations, scrutiny of defence spending, legislative challenges and public hearings could all increase the political cost of pursuing controversial foreign policy decisions.

The broader implication is that Trump may retain the authority to set America's foreign policy direction, but executing that agenda could become considerably more difficult.

With Democrats controlling both chambers, the final two years of Trump's presidency are likely to see a more confrontational relationship between the White House and Congress, with the consequences extending well beyond domestic politics.