Former Defense Secretary Robert Gates published an op-ed in the Wall Street Journal on Friday in which he criticized both major party nominees for their foreign policy, writing that neither “has said or done much to give anyone confidence.” He called out Clinton for her poor record in Libya, and her vague stances overall when it comes to national security, and described Trump as being “in a league of his own.”

Trump responded the following day on Twitter.

Never met but never liked dopey Robert Gates. Look at the mess the U.S. is in. Always speaks badly of his many bosses, including Obama.

— Donald J. Trump (@realDonaldTrump) September 17, 2016

While Clinton didn’t address the op-ed itself, she did criticize Trump’s initial reaction to it.

Presidential. https://t.co/tlfpcbVqkT

— Hillary Clinton (@HillaryClinton) September 18, 2016

Trump then talked about the op-ed during a rally in Colorado on Saturday:

We had a clown today, an absolute clown, Robert Gates. He’s supposed to be an expert. He’s been there forever… and he goes out and he says negative things about me. I never met him. I never talked to him. Believe me, I am so much better at what he’s doing than he is.

In the op-ed Gates points to Trump’s “record of insults to servicemen, their families and the military.” In the past the candidate has demeaned John McCain’s status as a war hero saying, “I like people who weren’t captured.” Following the Democratic National Convention, he slighted a Gold Star family by making incorrect assumptions about their religion. He has also claimed to “know more about ISIS than the generals do,” and he has advocated fighting the terror organization by targeting their families.

While Gates says that Clinton still has time to develop her policies and establish trustworthiness, he believes that Trump is “beyond repair.”

Neither of the candidates’ campaigns could immediately be reached for comment.