WASHINGTON — Immediately after President Trump ordered the killing of Maj. Gen. Qassim Suleimani of Iran, some of the loudest applause was heard from Pete Hegseth, a Fox News host and a decorated veteran of the Iraq and Afghanistan wars.
“He’s a terrorist who has killed Americans. We knew where he was and the president took a bold move to get rid of him, and people around the globe are thankful for that,” Mr. Hegseth said on the set of “Fox & Friends,” a perch he often takes to validate — and at times influence — Mr. Trump’s military policies.
That was the same Mr. Hegseth who has defended the president’s cozy interactions with Kim Jong-un, embraced Mr. Trump’s “America first” agenda of withdrawing forces abroad — and reversing interventionist policies he labeled irresolute and shameful — and energetically taken up the cause of combat veterans accused of war crimes.
But at no point during Mr. Trump’s presidency has Mr. Hegseth loomed larger, with the United States on a war footing and the next step unknown. Among the president’s unofficial policy advisers and those who add to the echo chamber on Fox News talk shows, no one else channels Mr. Trump’s mix of avowed isolationism, impulsive interventionism and unexpected resort to force.
“If I was part of shaping the narrative” concerning the strike on General Suleimani, Mr. Hegseth said in a telephone interview on Monday, “well, that’s a wonderful part of my day job.”
Mr. Hegseth’s views, which have greatly evolved since his time in the Army and his tenure leading two conservative veterans organizations, are emblematic of the seismic shift among many Republicans under Mr. Trump on long-held foreign policy positions. They also reflect a slow but significant souring among veterans on the post-9/11 conflicts that many believe have cost the nation too much in lives and money.
“I think a lot of us who were very hawkish and believe in American military might and strength were very resistant to how candidate Trump characterized the wars,” Mr. Hegseth said in another recent telephone interview. “But if we are honest with ourselves, there is no doubt that we need to radically reorient how we do it. How much money have we invested, how many lives have we invested and has it actually made us safer? Is it still worth it?”
Mr. Hegseth’s influence was most pronounced late last year when he lobbied heavily on behalf of Chief Petty Officer Edward Gallagher, a member of the Navy SEALs who was acquitted of serious war crimes. Mr. Trump reversed a demotion ordered as punishment, and then fired the secretary of the Navy, whom Mr. Hegseth had aggressively criticized.
Mr. Hegseth took to Fox News in November to defend Chief Gallagher. “From the beginning, this was overzealous prosecutors who were not giving the benefit of the doubt to the trigger pullers,” he said.
He spoke to Mr. Trump several times about the case. Mr. Trump subsequently tagged Mr. Hegseth in tweets on the issue, a public confirmation of his interactions with the president.
Having been successful in the Gallagher case, Mr. Hegseth has now taken up the cause of winning pardons for the Blackwater security contractors who were found guilty in the 2007 shooting of dozens of unarmed Iraqis in Baghdad.
Mr. Hegseth’s shift has alienated some longtime allies.
“I respect his service,” said William Kristol, a conservative analyst and former mentor to Mr. Hegseth. “I knew him 10 years ago and hoped he would be one of many leaders of that generation for strong American policy. But he has now apologized for war crimes and is a demagogue for Trump.”
Mr. Hegseth’s rallying around Mr. Trump’s order to attack General Suleimani has turned off some opponents of the “forever wars” who see opportunism. Voices like Tucker Carlson, another Fox host who has become strongly antiwar, and Concerned Veterans for America, a conservative group that Mr. Hegseth once led, have remained true to their war fatigue. Not Mr. Hegseth.
“I have been debating Pete Hegseth for 12 years, and I can’t tell you what he stands for other than himself and his own ambition,” said Jon Soltz, who served as an Army officer in the Iraq war and is a founder of VoteVets, a liberal group that advocates for veterans.
In 2009, Mr. Hegseth defended the surge in Afghanistan in repeated debates with Mr. Soltz, who was a critic of President Barack Obama and warned at the time that Iran was becoming empowered in Iraq.
“I don’t share the concern that President Trump is dragging us into endless war here,” Mr. Hegseth said. “In fact, I hate the term ‘endless war’ as it pertains to Iran.”
The transformation of Mr. Hegseth — an Ivy League-educated, decorated Army platoon leader and former ally of Senator John McCain — from fierce advocate of militarism abroad to passionate Trumpist trumpet is a symbol of the Republican Party in the Trump era.
Scores of buttoned-up, Russia-deploring free traders with a deep reserve of tolerance for military involvements abroad have cast aside core beliefs to embrace Mr. Trump, their new personas validated and amplified by the heavily groomed, assembled supporters on the Fox set, where Mr. Hegseth now sits.
He has scored the rare dual posts of cable star and unofficial Trump adviser; Mr. Trump considered him for the jobs of White House press secretary and secretary of veterans affairs.
Mr. Hegseth, a Minnesota native, graduated from Princeton University, where he was the publisher of The Princeton Tory, a conservative magazine for which he wrote about seeing the statue of Saddam Hussein toppled in Baghdad. “Conservative ideas have worked, do work and will continue to work,” he concluded. “The list is long: A strong military is absolutely essential to bringing long-term peace and stability to the world.”
After earning his Army commission via Princeton’s Reserve Officers Training Corps, he served with a National Guard unit guarding detainees at Guantánamo Bay in 2004 and 2005.
“He was a highly disciplined, highly focused, very intelligent officer and soldier who was really committed to serving his country,” said Ziad Shehady, who served with Mr. Hegseth.
In 2005, Mr. Hegseth volunteered to deploy to Iraq and was assigned to the Third Brigade of the 101st Airborne Division. There, Mr. Hegseth served under Col. Michael D. Steele, a hard-charging Army Ranger officer who was part of the Black Hawk Down episode in Somalia, a leader devoted to aggressive tactics to ferret out and kill suspected terrorist operatives, recorded on “kill boards” on base.
After Mr. Hegseth left, Colonel Steele oversaw Operation Iron Triangle, after which three American soldiers were convicted of murder for killing Iraqi prisoners. Colonel Steele was formally reprimanded but did not face charges.
“On that tour my eyes were open,” Mr. Hegseth said. “I was exposed to the reality of human nature, a vicious enemy, and I was forged and taught by these incredible patriots and warriors.”
Colonel Steele “understood the warrior ethos was very real,” Mr. Hegseth said, and under his command, he learned that “you subdue violence with violence.”
The experience helped shape his views of men accused of war crimes, said Mr. Hegseth, who has advised that “guys who make tough choices on the battlefield be given the benefit of the doubt.”
Pentagon and military leaders have said that Mr. Trump’s decisions could greatly reduce their ability to enforce discipline and could weaken the chain of command among the 1.3 million Americans on active duty.
Mr. Hegseth vehemently disagreed with that view, his single flash of anger during a lengthy interview. “You can maintain good order and discipline without throwing warriors under the bus,” he said, adding, “I think most of these characterizations are made by people who have never been in the type of situation that Gallagher has been in.”
If endorsing strong-arm tactics while opposing a conservative military strategy seems complicated, that is the new normal under Mr. Trump.
“When you get caught up in a movement, sometimes you promote things that make emotional sense at the moment but don’t really make any sense overall,” said Wade Zirkle, a Denver businessman and veteran who founded the pro-interventionist Vets for Freedom, then recruited Mr. Hegseth to take over.
Mr. Zirkle credits Mr. Hegseth with raising money and the organization’s profile but was surprised by his populist turn. “He is enabling the president who has no respect for the military or respect for U.S. alliances abroad,” Mr. Zirkle said.
After Mr. Obama announced the Afghanistan troop increase, Mr. Hegseth volunteered to deploy to Kabul in 2011 and 2012. As a senior counterinsurgency instructor, “I saw the clear disconnect between our strategy and reality,” he said. “We were selling a connect-with-the-locals message even though we knew that was not working.”
Mr. Hegseth left the military early to run for the Senate in Minnesota but withdrew when he lost ground to a Tea Party candidate who then lost the general election. He earned a master’s degree in public policy from the John F. Kennedy School of Government at Harvard University, then became the leader of Concerned Veterans for America, an advocacy group with ties to Charles Koch that has also been influential on Mr. Trump’s views of veterans health care.
Mr. Hegseth found the president’s ear and more attention from Fox News bookers. “It was never my intention to forge a relationship” with the president, he said. “I know that I have learned a great deal from the truths he has told, his courage on these issues to speak plainly and truly about topics that are usually spoken about in code.”
Over the last year, Mr. Hegseth has seemed to move further and further from the bookish veteran of his initial television appearances. He was recently banned from Twitter — where he has expressed support for the conspiracy theorist Laura Loomer’s congressional campaign and retweeted the cartoonist Ben Garrison, who has been called anti-Semitic — for posting part of a manifesto written by a Saudi aviation student who killed three people at Naval Air Station Pensacola.
Mr. Hegseth has also earned criticism with some of his Fox commentary supporting Mr. Trump’s more incendiary moments. He defended the president’s comments after the 2017 rally in Charlottesville, Va., during which a white nationalist killed a protester by crashing his car into the crowd.
“There’s a reason those people were out there,” he said. “Some of it is outright racism and needs to be condemned. A lot of it, though, is I feel like my country is slipping away and just because I talk about nationalism, not white nationalism, doesn’t mean I’m talking in code, that I’m a racist.”
Despite his criticism of many conflicts overseas, Mr. Hegseth recently rejoined the Army as a commissioned major in the National Guard in Washington. From there, he could face deployment to a conflict with Iran.
“We are in a generational struggle against radical Islam,” he said.
“I wouldn’t put my views in a libertarian box or neocon box,” he concluded. “I believe in putting America first.”