US President Donald Trump has challenged Rex Tillerson to “compare IQ tests” if his secretary of state did indeed ever call him a “moron”, as reported.Trump told Forbes magazine: “I think it’s fake news. But if he did that, I guess we’ll have to compare IQ tests. And I can tell you who is going to win.” He made the comment while speaking to the magazine on Friday. A story was published online on Tuesday.Trump’s tense relationship with Tillerson burst into public view last week. An NBC News story claimed vice president Mike Pence had to talk Tillerson out of resigning this summer, and that Tillerson had called Trump a “moron.”Tillerson said he never considered resigning. His spokeswoman said he never used such language. Trump and Tillerson are scheduled to have lunch on Tuesday with defence secretary Jim Mattis.