Retired Marine Gen. James Mattis, President-elect Donald Trump’s choice for defense secretary, has ruffled feathers within the Obama administration with his controversial opinions on women in combat and post-traumatic stress disorder.

The former head of U.S. Central Command has said in various speeches that women may not be suited for the “intimate killing” of combat, and allowing men and women to work in close quarters would be detrimental to their success in combat zones, according to Military.com. 

In his remarks at the Marines’ Memorial Club in San Francisco in 2014, Mattis tried to explain his line of thinking. “The idea of putting women in there is not setting them up for success,” he said, referring to combat as an “atavistic primate world.”

“It would only be someone who never crossed the line of departure into close encounters fighting that would ever even promote such an idea,” he added, stressing that whether women can handle the physical rigor of combat is beside the point.

There was a significant amount of pushback from the Marine Corps after current Pentagon chief Ashton Carter made the historic announcement last year opening up all combat roles to women. 

Mattis has also argued there is a pervasive “fixation” in the military regarding post-traumatic stress disorder.

“If we tell our veterans enough that this is what is wrong with them they may actually start believing it,” Mattis said during the same event in San Francisco.

Before submitting to confirmation hearings, Mattis must first obtain a special waiver allowing him to bypass the rule blocking military personnel from accepting posts requiring Senate confirmation for seven years after retirement.

Mattis retired as a four-star general in 2013. 

Trump announced Mattis’ nomination at a victory rally Thursday in Ohio.