The photograph showed a smiling cadet receiving a medal from an instructor on the final day of training. By Tuesday the post had drawn more than 5.4 million views.
"Just a vile, insecure scumbag and a disgrace to the US military," wrote Ron Filipkowski, the editor of MeidasTouch.
The post went up the same day Hegseth's top Army official quit. Army Secretary Dan Driscoll resigned Monday after 18 months in the job, the White House confirmed. The Wall Street Journal first reported his departure.
Driscoll's departure leaves the Army without a top civilian leader, a Senate-confirmed top general, a confirmed general in charge of operations, or a confirmed commander of troops in Europe, according to The Atlantic.
The service has more than 450,000 active-duty soldiers. It now has fewer generals than at any point in recent history, the magazine reported.
One source familiar with the assessment told the Post that military leaders view the six-month war as "too much for too long," the Daily Mail reported.
That was the backdrop former Alberta premier Jason Kenney pointed to.
"In the midst of a hot war against a mortal enemy of the United States, the Secretary of War of the world's only super power finds time to troll folks at a cadet camp for teenagers in Vernon, British Columbia," Kenney said in a post quoted by Newsweek.
"To our many friends in the great United States of America: what's going on?" he added.
Canada's Cadet Program is open to young people aged 12 to 18, according to the Department of National Defence. The Vernon centre runs summer training in leadership and drill.
Cadets are not members of the Canadian Armed Forces, the department says.
The adult in the photograph holds a different status again. Instructors in the Cadet Instructors Cadre are reserve officers whose primary duty is supervising and training cadets, not operational service.
"This is a picture of two women from the Vernon Cadet Training Centre, which holds summer programming for 12-18 year olds to develop skills on the way to adulthood. Unlike Secretary Hegseth, they do not deserve contempt or ridicule," wrote Connor Ewing, a political scientist at the University of Toronto.
American critics made the same point about the ages involved.
"Literally they're kids. This is a cadet program and our a-- hat of a Secdef is making fun of children," wrote Adam Kinzinger, a former Republican congressman from Illinois and an Air National Guard officer.
"MAGA males are betas who have to punch down to feel big," Kinzinger continued.
"158 Canadians gave their lives fighting alongside the Americans in Afghanistan. Have some respect, you absolute lowlife," wrote Shannon Phillips, reaching independently for the same figure.
Phillips served as Alberta's environment minister in Rachel Notley's government and won three elections in the province's south.
A Canadian journalist Terry Reith called Hegseth's post reprehensible: "Am I seeing this right. Is the US secretary of defence trying to shame cadets in Vernon? These are cadets, high school kids."
Hegseth's conduct in office has drawn sustained criticism. Guardian columnist Margaret Sullivan pointed to his "bloodthirsty utterances, his fierce loyalty to Trump and his appalling inability to manage this huge moment in world history" to conclude he was a "disaster".
Hegseth told military leaders last September that he no longer wanted to see "fat generals and admirals" or overweight troops, the Daily Beast reported.
He spent his first months in office firing senior women leaders and cancelled the Women, Peace and Security Program that Trump began in his first term, according to the American Civil Liberties Union.
He also eliminated the Defense Advisory Committee on Women in the Services, a body created in 1951 that had advised the Pentagon for more than 70 years. A Pentagon spokesperson called it a "divisive feminist agenda that hurts combat readiness," the organization said.
At Quantico last fall, Hegseth ordered combat standards returned to what he called the highest male standard, the group said. Women already meet gender-neutral requirements in those roles and make up roughly 18 percent of service members.
"If women can make it, excellent. If not, it is what it is," Hegseth said in those remarks.
Another Trump cabinet official mocked Canada's military the same day.
"I mean, we're not at war with Canada. How are we going to be at war with Canada? What, they're going to take their two submarines from the Edmonton Mall and sic them on us?" Treasury Secretary Scott Bessent said on CNBC, according to Newsweek.
Canada has four Victoria-class submarines and has selected a German supplier for a replacement fleet of up to 12, the outlet reported.
The remarks landed during a deepening trade dispute. Prime Minister Mark Carney suspended negotiations with Washington in August after calling American demands unfair, and Trump imposed 50 percent tariffs on hundreds of Canadian goods.
Canadian voters delivered their own answer Monday. Carney's Liberals won all three federal special elections held that day, including a Quebec seat the Conservatives had held since 2018.
