President-elect Donald Trump this week tapped Pete Hegseth to be his secretary of defense -- despite the Fox News host having previously criticized Trump on his foreign policy and military stances before Trump was elected to his first term.

During Trump's 2016 campaign, Hegseth, appearing on Fox News as a political commentator, slammed what he characterized as Trump's "shallowness" on foreign policy.

"As far as Donald Trump, he is just flat out changing his position, and I think, frankly, falling into the narrative of the left. And he's done this time and time again." Hegseth said. "He's going back and forth. He's been good on a lot of domestic stuff. But internationally, I don't know where Donald Trump is."

The comments came as Hegseth was pressed during an interview by then-Fox News host Megyn Kelly -- who would later, after leaving Fox News, endorse Trump's 2024 candidacy -- about Trump's "obvious reversal" of his position on the war in Afghanistan.

"It's unacceptable. It shows, I think, a shallowness in his understanding of that region," Hegseth said, pointing to Trump's comments that the U.S. could remain in the region endlessly. "That's not clarity, that's not leadership -- that's waffling back and forth on really critical issues."

A former Army major who served in Iraq, Afghanistan, and as a guard at Guantanamo Bay, Hegseth has since emerged as one of Trump's most vocal allies in cable news. He previously led two veterans' organizations before transitioning fulltime to his position at Fox News.

After his initial criticism, Hegseth fell in line with Trump during the 2016 general election and has continued to be one of his most enthusiastic boosters on television.

Trump and Hegseth have brokered a close relationship in recent years, with Hegseth interviewing Trump multiple times and reportedly engaging with Trump during commercial breaks on the program he anchors, Fox & Friends Weekends.

In an ironic twist, Hegseth in 2015 criticized Trump for saying during an interview that he gets some of his military advice from watching television news.

"You wouldn't want a top-tier presidential candidate getting all their military advice from watching 'Meet the Press,'" Hegseth said during a Fox News interview. "There's a lot more nuance and there's a lot more detail ... at the end of the day, foreign policy and national security is not about TV shows. It's a complex web of relationships and I think [his campaign] is going to want him briefed on that kind of stuff."

While appearing on NBC's "Meet the Press" in August 2015, Trump was asked by moderator Chuck Todd who he talks to for military advice.

"Well, I watch the shows. I mean, I really see a lot of great -- you know, when you watch your show and all of the other shows and you have the generals and ... you have certain people that you like," Trump responded, according to a transcript.

Hegseth has since taken a sharp turn to become a fierce ally and defender of Trump.

"People outside these walls ... they don't understand the attachment that conservatives and freedom lovers have to Donald Trump," Hegseth said in a clip he posted of himself speaking in 2023 at the Conservative Political Action Conference.

Previously, Hegseth had said he supported other candidates for president early on in the 2016 race.

"I had different candidates I believed in early on in the process, and was critical of the early things [Trump] had to say," Hegseth told a Jewish newspaper in 2016. "I still don't like some of his rhetoric."