Donald Trump derided former Defense Secretary Robert Gates, calling the national security official a 'clown' and a 'mess.' The attacks came after Gates expressed concern about Trump's readiness to be commander-in-chief. Gates, who served under both Republican and Democratic presidents, wrote that both Trump and Hillary Clinton 'have a credibility problem in foreign affairs' before singling out the Republican nominee as 'in a league of his own' and 'beyond repair' on security issues. 'We had a clown today, an absolute clown, Robert Gates,' Trump told a crowd. 'He's supposed to be an expert. He's been there forever ... 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.'