Democrats plan to reject President Donald Trump's proposed $1.5 trillion defence budget and investigate the Pentagon and the war against Iran, after winning both chambers of Congress in the midterms.

Representative Adam Smith, the top Democrat on the House Armed Services Committee, outlined the plans on Thursday. "We must push for the development of a more realistic and sustainable approach to our national security, one that does not require a defense budget in excess of $1 trillion or one paid for with draconian cuts to critical domestic programs," Smith said.

Trump's $1.5 trillion request is the largest defence budget in American history. The House and Senate authorisation bills each carry about $1.15 trillion, and the appropriations measure about $1.07 trillion. The administration had planned to add $350 billion through reconciliation, but that route is now expected to fail.

Iran war oversight

Smith also pledged oversight of the war in Iran. "The list of potential oversight topics is long, but the illegal war against Iran is top of mind for me and the American people," he said. Democrats have refused to back the administration's Iran war funding request without guardrails or an exit strategy.

War Secretary Pete Hegseth has defended the request, telling lawmakers that not funding the department at that level would be "the greatest threat that our nation faces." The administration says the money would rebuild stockpiles depleted in the Iran conflict and fund the Golden Dome missile defence system.

Democrats' power to stop the war itself is limited: Trump could veto any halt order, and overriding a veto needs two-thirds majorities in both chambers. But they can refuse new funding, although money already appropriated could remain available. Federal funding currently runs only until 11 December under a continuing resolution.