Former Defense Secretaries Leon Panetta and Robert Gates speak at the Reagan National Defense Forum "Building Peace Through Strength for American Security" event at the Ronald Reagan Presidential Library & Museum in Simi Valley, Calif. | Getty Gates questions Clinton's 'judgment' on emails

Hillary Clinton's decision to use a private email server to conduct official business at the State Department was an "error in judgment," former Defense Secretary Robert Gates said on Thursday.

"I don't know what originally prompted her to think that was a good idea," the former defense secretary and CIA director told Yahoo News' Katie Couric in a livestream interview.


Gates also said he has not had a conversation with Clinton since he left the administration in 2011.

"The only communication I had from her was when I broke my neck, she just sent me wishing me well and to follow the doctor's orders," Gates recalled.

When it comes to presumptive Republican nominee Donald Trump, Gates said, "not right now, no," when asked whether he would be comfortable with Trump his finger on the nuclear button.