Pete Hegseth is increasingly looking like he may take the fall for Republicans’ midterm losses, despite Donald Trump’s vocal support for his defense secretary, even calling him a champion of war.

The war in Iran, which voters and Trump have named as a key reason for Republicans’ midterm losses, “has been primarily a Department of War-led effort because you chose to take military action to resolve a foreign policy matter”, a former senior Pentagon official told CNN.

“If the president is serious about anyone taking responsibility for it, it’s Pete Hegseth,” one Republican close to the White House added in an interview with CNN. “Pete has been either dishonest or incorrect – neither of which are acceptable – about timelines, goals and objectives since the beginning.”

On Wednesday, JD Vance publicly questioned whether the Iran war was worth it and said it cost Republicans control of Congress.

Thomas Massie, a Republican congressman from Kentucky, has already filed eight impeachment accusations against Hegseth, and plans to soon force a House vote on the impeachment.

Trump has repeatedly defended Hegseth and, in speaking with reporters on Wednesday about whether he was considering replacing Hegseth, said: “No, I think ⁠he’s doing a very good job.”

Kingsley Wilson, the Pentagon press secretary, said: “The entire Department is unified behind the Secretary’s vision and will continue working to put our warfighters and America first,” in a statement to USA Today on Wednesday.

Trump has described Hegseth as a key proponent of the unpopular conflict, saying on 23 March: “Pete, I think you were the first one to speak up, and you said: ‘Let’s do it, because you can’t ⁠let them have a nuclear weapon.’”

Hegseth has been a polarizing figure in American politics and has made enemies even with his own Republican party.

Thom Tillis, the Republican US senator, told CBS News on Tuesday night that Hegseth had “a reckoning” coming and his strained relationship with lawmakers was undermining the Trump administration’s push for a $1.5tn defense spending package in Congress.

“I think after the election, we need to determine whether or not he’s the best person to bring those needs to Congress if he wants something done before the end of this Congress, which is only 60 days away,” Tillis said as the midterm results came in.

Democrats have promised to investigate Hegseth and his handling of the Pentagon, and aides say that could include everything from his handling of the Iran war to his purges of top military officers, including the chair of the joint chiefs of staff.

He could also face ‌scrutiny over his Ukraine policy and US military strikes on alleged drug-trafficking boats in Latin American waters, which some Democrats say could amount to war crimes.

Adam Smith, the Democratic representative who is expected to lead the House armed services committee next year, promised vigorous oversight on everything from the Iran war to what he called the erosion of the “apolitical foundation of the armed forces”.