More: "Here's the problem with Trump," Hegseth said in an appearance on Megyn Kelly's show that night. "He says, Go ahead and kill the family. Go ahead and torture. Go ahead and go further than waterboarding.'"

"What happens when people follow those orders, or don't follow them? It's not clear that Donald Trump will have their back," Hegseth added. "Donald Trump is oftentimes about Donald Trump. And so you can't; if you're not changing the law and you're just saying it, you create even more ambiguity."

Hegseth argued the US could fight ruthlessly without abandoning its moral footing and warned that Trump's rhetoric risked pushing troops past that line.

"What Donald Trump is doing here, though, creates more complications I think on the backend for a lot of our folks," he said.