U.S. President Donald Trump on Wednesday acknowledged that the war with Iran was a major factor behind Republicans' crushing midterm election losses, echoing Vice President JD Vance's call for the party to confront the political fallout from the increasingly unpopular conflict.

Asked if he agreed with Vance's remark that the Iran war was "the reason we lost," Trump, speaking to reporters at his White House ballroom construction site, said: "I think it's largely true because it drove the gasoline up a little bit short term."

"But at the same time, if I had it to do again, I'd have to do it again. Because long term, it's the only answer. You can't let Iran have a nuclear weapon," he added.

The midterm election blowout delivered a new era in Washington, with Democrats in Congress eager to meet voter demands for change while Republicans watched their majorities evaporate after a revolt against President Donald Trump and his party in power.

Democrats ousted Republicans from coast to coast, with many surprising places in between, in a decisive rejection of unified GOP control for the promise of something different for the country. Their majorities will be padded by unusually wide margins in both the House and the Senate.

The staggering results are setting up a starkly divided government, with an emboldened Congress poised to reassert itself as a coequal branch when Democrats take over in the new year. They are ready to launch a 100-day agenda to lower the costs of gas, groceries and healthcare and conduct vast oversight and investigations into Trump and his administration, with impeachment an option.