Even before he disclosed secret battle plans for Yemen in a group chat, information that could have endangered American fighter pilots, it had been a rocky two months for Defense Secretary Pete Hegseth.

Mr. Hegseth, a former National Guard infantryman and Fox News weekend host, started his job at the Pentagon determined to out-Trump President Trump, Defense Department officials and aides said.

The president is skeptical about the value of NATO and European alliances, so the Pentagon under Mr. Hegseth considered plans in which the United States would give up its command role overseeing NATO troops. After Mr. Trump issued executive orders targeting transgender people, Mr. Hegseth ordered a ban on transgender troops.

Mr. Trump has embraced Elon Musk, the billionaire chief executive of SpaceX and Tesla. The Pentagon planned a sensitive briefing to give Mr. Musk a firsthand look at how the military would fight a war with China, a potentially valuable step for any businessman with interests there.

In all of those endeavors, Mr. Hegseth was pulled back, by congressional Republicans, the courts or even Mr. Trump.

The president made clear last Friday that he had been caught by surprise by a report in The New York Times on the Pentagon’s briefing for Mr. Musk, who oversees an effort to shrink the government, but also denied that the meeting had been planned.

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