Pete Hegseth has failed to give Donald Trump an accurate picture of the war on Iran while resorting to “dangerously exaggerated” statements to create an inaccurate picture of a US military triumph, a senior Democrat told a Capitol Hill hearing on Thursday.

Jack Reed, the ranking Democrat on the Senate armed services committee, told Hegseth, the defense secretary, that far from victory, US citizens were having to bear the cost of a war they did not support in the form of increased fuel prices.

“American families are bearing the cost of a war they wanted nothing to do with and have gained nothing from and yet, Secretary Hegseth, you declared victory a month ago,” said Reed, a senator from Rhode Island.

The comments came at the opening of the second successive day of congressional testimony from Hegseth and Dan Caine, the chairman of the US armed forces’ joint chiefs of staff, who are testifying over the Pentagon’s record $1.45tn military budget submission.

As with the previous day’s appearance before the equivalent committee in the House of Representatives, the hearing quickly devolved into confrontation over the war with Iran, which has become stalemated after eight weeks of fighting and seen the regime in Tehran close the strategically vital strait of Hormuz.

Protesters briefly interrupted the hearing as Hegseth made an opening statement. Shouts of “war criminal” and “despicable” were heard before the protesters were expelled and proceedings resumed.

Reed immediately went on the offensive, accusing Trump of going to war without a “coherent strategy” while declining to “make a case to the American people or consult Congress”.

But his statement reserved the fiercest personal criticism for Hegseth, who stood accused of failing to give Trump essential information or advice, while pursuing a personal agenda as service personnel were injured or killed in battle.

“The problem with your statements, Mr Secretary, is they are dangerously exaggerated,” Reed said. “Iran’s hard line regime remains in place. It still retains stockpiles of enriched uranium, and its nuclear program remains viable.

“I am concerned that you have been telling the President what he wants to hear instead of what he needs to hear. Bold assurances of success are a disservice to both the commander in chief and the troops who risked their lives based on them. Our military has performed heroically, but military force without a sound strategy is a path to long-term defeat.”

Reed also seized on Hegseth’s often bellicose rhetoric, in which he has disparaged the need for rules of engagement and vowed to pursue Iranians “no mercy”.

“Too often you have made dangerous statements that are counterproductive to the mission you boasted about,” he said. “Quote, ‘no stupid rules of engagement’, just days after hundreds of Iranian school girls were tragically killed in a missile strike, you have made troubling statements about showing no mercy and no quarter to the Iranians orders that would constitute war crimes.”

He said that while US forces were in harms way Hegseth had devoted his time to personal priorities, including overhauling the Pentagon’s chaplain corps and services, cancelling flu vaccine requirements and barring service personnel from attending certain universities.

Reed also criticised Hegseth’s decision this week to invite the singer and rapper, Kid Rock, to an army base for what he called a “joy ride” on an Apache helicopter, as well as for firing multiple senior commanders – frequently on the basis of race or gender – and blocking the promotions of others.

“You are hollowing out our military defensive experience and highest performing senior officers while making young officers wonder if they should continue to serve,” he said.

Hegseth reprised criticisms he had made of Democrats and “some” Republicans at Wednesday’s hearing, when he had called critics of the war effort “reckless, feckless and defeatist”.

“As I said yesterday, and I’ll say it again today, the biggest adversary we face at this point are the reckless naysayers and defeatist words of congressional Democrats and some Republicans,” he said.

He dismissed critics as “defeatists from the cheap seats who two months in, seek to undermine the incredible efforts that have been undertaken and the historic nature of taking on a 47-year threat with the courage no other President has had, to great success and great opportunity for preventing Iran from having a nuclear weapon”.