Brash and bellicose, he sounded more like a cartoon bully than a sombre statesman. “Death and destruction from the sky all day long,” Pete Hegseth, wearing a red, white and and blue tie and pocket square, bragged to reporters at the Pentagon near Washington. “This was never meant to be a fair fight, and it is not a fair fight. We are punching them while they’re down, which is exactly how it should be.”

Hegseth, 45, a former Fox News TV host who now commands the world’s most powerful military, has this week become the face of Donald Trump’s war in Iran. That has set off for alarm bells for critics who warn that the Secretary of Defense – pointedly rebranded “Secretary of War” – has rapidly transformed the Pentagon into the staging ground for an ideological and religious crusade.

With machismo, Christian nationalism and callousness toward the lives of US troops, they say, Hegseth’s puerile displays on TV are aimed at sating Trump’s desire for a warmonger worthy of the manosphere. This was reinforced by a lurid social media video that intersperses clips from Hollywood blockbusters such as Braveheart, Gladiator, Superman and Top Gun with Hegseth and real kill-shot footage of the attacks in Iran.

Janessa Goldbeck, chief executive of Vet Voice Foundation, a nonprofit advocacy organisation, said: “Pete Hegseth is a very dangerous person. He’s a white Christian nationalist and has the arsenal of the United States government at his disposal and a permission slip from President Trump to deploy carnage wherever he wishes against whomever he wishes.”

Hegseth’s rise would have been unthinkable under any other commander-in-chief. Born in Minneapolis, he studied politics at Princeton University and became publisher and editor of the Princeton Tory, a conservative student journal, where he frequently waded into culture-war issues such as feminism and homosexuality.

After leaving Princeton, Hegseth joined the US army national guard as an infantry officer. His service included deployments to Guantánamo Bay in Cuba and tours of Iraq and Afghanistan. He later revealed in a book that he told soldiers under his command in Iraq to ignore legal advice about when they were permitted to kill enemy combatants under their rules of engagement.

Hegseth became chief executive of Concerned Veterans for America, a conservative advocacy group, but departed in 2016 amid allegations of financial mismanagement, sexual impropriety and personal misconduct.

In 2018 Hegseth’s mother, Penelope, sent him an email that said: “You are an abuser of women – that is the ugly truth and I have no respect for any man that belittles, lies, cheats, sleeps around, and uses women for his own power and ego. You are that man (and have been for years) and as your mother, it pains me and embarrasses me to say that, but it is the sad, sad truth.”

Hegseth subsequently became a familiar face on TV as a contributor and co-host of Fox & Friends on Fox News, frequently interviewing Trump and defending his policies. He once wrote that, in the event of a Democratic election win, “the military and police … will be forced to make a choice” and “Yes, there will be some form of civil war”.

But Trump prevailed in 2024 and nominated Hegseth to serve as secretary of defence. At his confirmation hearing, senators raised serious questions about his record: disparaging remarks about women serving in the armed forces; allegations that he drank while on duty; claims of sexual assault and misconduct; his troubled tenure running two small veterans’ nonprofit organisations; and his lack of experience for a post overseeing the world’s most powerful military.

The Senate ultimately split 50–50, forcing the vice-president, JD Vance, to cast the tie-breaking vote. As defence secretary Hegseth has vowed to “unleash overwhelming and punishing violence” on enemies and promised to dispense with “stupid rules of engagement” – rules designed to restrict attacks on civilian populations.

Now, in his first week guiding the nation through a murky new Middle East conflict, Hegseth has largely forgone the solemnity of a traditional defence secretary in favour of the performative antics of a partisan broadcaster revelling in America’s capacity to inflict violence.

For years he had cultivated a hypermasculine “muscleman” aesthetic designed to play to Trump’s sensibilities and the rightwing media ecosystem. Now, faced with a geopolitical crisis that demands nuance and strategic foresight, he appears to many to be out of his depth.

Goldbeck, a Marine Corps veteran who was deployed overseas as a combat engineer officer, commented: “I wish I could say how cavalier, obtuse and hopeless Secretary Hegseth is at leading the Pentagon. I can’t even muster the words to describe his self-adulation, matched only in scope by his apparent moral depravity.”

She added: “Let’s not forget that Pete Hegseth is a former morning-show Fox News TV host, and has this cartoonish persona, speaking what he thinks is tough-guy language, but sounds to me as a veteran and to many of my peers who served in combat like somebody who is completely inept and pretending to have this macho persona.

“Honestly, it’s embarrassing. We know this guy is incompetent. I wouldn’t feel safe leaving Pete Hegseth in charge of putting together a DoorDash order.”

Former White House officials share the concerns. Brett Bruen, president of the public affairs agency Global Situation Room and former global engagement director of the Barack Obama administration, said: “Hegseth is ill-suited for the kind of reassurance and strategy that Americans and our allies need to hear from the Pentagon right now.

“They don’t need a bumper sticker. They don’t need the bravado and the brashness that he brings. They need to know that America’s military is in strong, stable hands and what we have seen in his first couple of war press conferences is an inability to move beyond this Fox personality and into the role of leader of our nation’s military at a time of war.”

During his Pentagon briefing on the war on Wednesday, Hegseth adopted a bombastic tone, saying of Iranian leaders: “They are toast and they know it. Or at least soon enough they will know it. America is winning – decisively, devastatingly and without mercy.”

He bashed “fake news” while addressing the six army reservists killed in an Iranian attack on an operations center in Kuwait. “When a few drones get through or tragic things happen, it’s front-page news. I get it. The press only wants to make the president look bad. But try for once to report the reality. The terms of this war will be set by us at every step.”

The comments provoked uproar for their lack of empathy for America’s fallen. Jeremy Varon, a history professor at the New School for Social Research in New York, said: “That’s outrageous. You have a national effort by all media regardless of partisan bent to memorialise and honour the dead and he sees that simply as a tactic to bring down Trump.”

There was another aspect of Hegseth’s personality barely addressed by the Senate: his sympathy for Christian nationalism. Photos have shown him bearing two tattoos associated with crusader imagery. One depicts the Jerusalem cross – a cluster of five crosses long connected to medieval crusader iconography – on his chest.

Nearby is an image of a sword accompanied by the Latin phrase “Deus vult”, meaning “God wills it”, a slogan historically linked to the crusades and revived in recent years by various far-right groups. It appeared on clothing and flags carried by some participants in the January 6 Capitol attack.

Nor are the references merely symbolic. In his 2020 book, American Crusade, Hegseth wrote that those who benefit from “western civilisation” should “thank a crusader”. The book suggests that democratic politics alone may not suffice to achieve the goals of his political allies, declaring: “Voting is a weapon, but it’s not enough. We don’t want to fight, but, like our fellow Christians one thousand years ago, we must.”

There have been reports of more troubling behaviour. The New Yorker reported that a colleague at Concerned Veterans for America complained that he and another man repeatedly shouted “Kill all Muslims!” during a drunken episode at a bar while travelling for work.

Hegseth has previously endorsed the doctrine of “sphere sovereignty”, a worldview derived from the extremist beliefs of Christian reconstructionism (CR). The philosophy calls for capital punishment for homosexuality and strictly patriarchal families and churches.

The defence secretary attends Pilgrim Hill Reformed Fellowship, a church linked to the Communion of Reformed Evangelical Churches, a denomination co-founded by the pastor Doug Wilson, who has openly advocated a theocratic vision of society in which wives should submit to their husbands and women should be denied the vote. Wilson recently led a worship service at the Pentagon at Hegseth’s invitation.

Robert P Jones, president and founder of Public Religion Research Institute thinktank in Washington, said: “This is not one or two comments. It’s not a kind of one-off behaviour. This is like a longstanding publicly demonstrated orientation that Hegseth has. It’s not just a glorification of violence but a glorification of violence in the name of Christianity and civilisation.”

The Military Religious Freedom Foundation (MRFF) says it has received more than 200 complaints from service members about military commanders invoking extremist Christian rhetoric about biblical “end times” to justify involvement in the Iran war. Such language could also be offensive to Arab allies and provide Iran with the fodder it needs to justify its own holy war against the US.

Jones warned: “It casts this not as anything related to the public – is it about a nuclear programme? Is it about sponsoring terrorism? – which are legitimate political concerns. It takes it out of the realm of politics and casts it as a holy war of a supposedly Christian nation against a Muslim nation.”

Doug Pagitt, a pastor and executive director of the progressive Christian group Vote Common Good, compares Hegseth’s worldview to the historical heresy of Constantine, who allegedly painted a cross on his shield to conquer in the name of God – a theology the broader Christian church has spent centuries trying to distance itself from following the horrors of the Crusades.

Pagitt said: “It seems to me that Pete Hegseth has a worldview, which is contorted toward thinking that this administration has a particular divine calling. He believes – because he said it – that God has uniquely ordained Donald Trump and those that he chooses to accomplish very specific purposes in the world.

“Pete Hegseth’s own version of Christianity is one that’s built around a certain Christian advancement that comes through the domination of the governments of nations. He believes that not only is the military at his disposal to use for his purposes but it’s there to fulfill God’s agenda for the world.”