White House Chief of Staff John Kelly may be positioning himself to stand his ground against President Donald Trump’s fiery temper, The New York Times reported on Friday.

After staff members cautioned Trump to tone down his rhetoric following a raucous campaign rally in Phoenix, Arizona, last month, he reportedly lashed out at Kelly, who offered a coolheaded response.

Privately, The Times’ Glenn Thrush and Maggie Haberman wrote, Kelly was incensed by Trump’s bite, telling White House staff he had never been spoken to in that way during his 35 years of military service, according to three sources familiar with the talk.

The Times’ sources also noted that Kelly said he would not condone the same treatment in the future.

After replacing former chief of staff Reince Priebus five weeks ago, Kelly immediately began regulating the White House, becoming an instrumental force in the dismissal of several controversial staffers, including former chief strategist Steve Bannon and former communications director Anthony Scaramucci.

Kelly, a career US Marine, has taken his fair share of criticism after stepping into Trump’s universe. Though White House officials have said there was no indication Kelly is looking for an out, he has reminisced about his tenure as a Marine.

“The best job I ever had was as a sergeant in the Marine Corps,” Kelly joked during a social dinner at Trump’s clubhouse in Bedminster, New Jersey, “and after one week on this job, I believe the best job I ever had is as a sergeant in the Marine Corps.”

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