“I never met former Defense Secretary Robert Gates. He knows nothing about me. But look at the results under his guidance - a total disaster!” the GOP presidential nominee tweeted.

I never met former Defense Secretary Robert Gates. He knows nothing about me. But look at the results under his guidance - a total disaster! — Donald J. Trump (@realDonaldTrump) September 17, 2016

In a subsequent tweet, Trump called Gates "dopey" and accused him of criticizing his bosses.

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

Gates specifically ripped Trump for “naive and irresponsible” expressions of admiration for Russian President Vladimir Putin, and for a Middle East plan he called a “dangerous approach oblivious to the reality” of the region.

“Mr. Trump is also willfully ignorant about the rest of the world, about our military and its capabilities, and about government itself,” he wrote.

“He disdains expertise and experience while touting his own — such as his claim that he knows more about ISIS than America’s generals. He has no clue about the difference between negotiating a business deal and negotiating with sovereign nations.”

Gates and Trump have gone after each other throughout the presidential campaign.