"The reason we lost is the war." With one post on X, US Vice-President JD Vance has broken with the Republican Party's official line and laid the blame for Tuesday's midterm defeat on the conflict with Iran that his boss started eight months ago.

Vance, widely seen as Donald Trump's heir and a likely candidate for the presidency in 2028, wrote that "the president himself said so last night" and that "any honest conversation about where we go from here must start there", Al Jazeera reports.

The post came as Democrats took control of both the House of Representatives and the Senate in what US networks describe as one of the most lopsided midterm results in modern history.

Voters who walked away

Vance cited a pollster's survey of people who backed Trump in 2024 but planned to vote Democratic this year. According to Al Jazeera and The National Desk, the four reasons they gave most often were ending the Iran war, the cost of living and inflation, putting America first and "changing our relationship with Israel".

CBS News also reports Vance saying the war is "the reason we lost". He has been one of the administration's negotiators in efforts to end the conflict and has often sounded more cautious about it than other senior officials.

Trump: 'I would have done it again'

Trump has not backed away. He told The Wall Street Journal that the war was "a piece of it" but that he had done the right thing. "I would have done it again," he said.

Asked about his deputy's post, Trump was reported as saying: "I think it's largely true because it drove the gasoline up a little bit short term." He said the long-term case still stood: "You can't let Iran have a nuclear weapon."

The Wall Street Journal's editorial board attacked Vance's framing, arguing that it ignored other factors such as tariffs and corruption claims and weakened Trump's hand in talks with Tehran, though it accepted that the war and high fuel prices played a part.

A former Bush-era deputy national security adviser, Mark Pfeifle, told Al Jazeera the lesson was simple: "If you mess up, fess up!"

Why it matters beyond Washington

The split is the clearest sign yet that the Iran war has become a political liability for Trump's camp, with the new Democratic Congress expected to use its power over spending to press for a wind-down. Iran has kept the Strait of Hormuz largely closed, keeping oil prices high around the world, including in fuel-importing countries such as Kenya.

Whether Vance's remarks push the White House closer to a deal, or open a rift at the top of the party ahead of 2028, is now the question in Washington.

Photos: Al Jazeera/AP (Tom Brenner, pool: JD Vance at Joint Base Andrews); Daniel Torok/White House via Wikimedia Commons (public domain, Donald Trump). Thumbnail design: HAMASTA MEDIA.