Former Secretary of Defense Robert Gates is not a fan of Donald Trump, and he has no problem telling the American people that the billionaire would be a mistake. On Sunday s episode of ABC s This Week, he did exactly that.Guest host Martha Raddatz asked Gates what he thought about the speech the Republican frontrunner gave on foreign policy earlier in the week and like former Secretary of State Madeleine Albright, Gates was not impressed: I think based on the speech you d have somebody who doesn t understand the difference between a business negotiation and a negotiation with sovereign powers. For example, he, on the one hand, says we need to be a more reliable ally to our friends. And then in the next breath he basically says we re going to rip up all those burden-sharing agreements that we ve had over the decades with them and make them go their own way if they don t pay for everything. During Trump s speech he did, in fact, contradict himself. He claimed he was going to take care of our allies, but then he said that many of them aren t paying their  fair share and if he were president he would make those countries (mostly in the Middle East)  defend themselves. Gates also slammed Trump for his inability to take advice: One of the things that worries me, Martha, is that he doesn t appear to listen to people. He believes that he has all the answers, that he s the smartest man in the room. And I ve worked with some   for some very different presidents. Jimmy Carter and Ronald Reagan, George W. Bush, Barack Obama. One of the things they all had in common was a willingness to listen to people who with   who had experience, and then make their own independent judgment. Now, they ve gone in different directions but they never assumed they had all the answers, and that s one of the things that troubles me. He definitely does think he knows best and that is a huge problem when you think about how much power he would have as president. Just look at his campaign, he continues to insult minorities and women even as other officials in his party tell him to knock it off. He continues to say that he will force other countries to pay for things, even though experts say that is not possible. What would happen if he were sitting in the White House and the Secretary of Defense told him that his plan to  bomb the hell out of ISIS  wasn t a good idea? Would he ignore his military advisers? The answer is: probably.When a person with as much experience as Robert Gates says Trump is a bad idea, the Republican Party should take him seriously.Featured image via Chip Somodevilla/Getty Images