Robert Gates, who served as defense secretary for the Obama administration, paused for a moment and said "I don't know" in an interview Sunday when asked if he thinks former VP Joe Biden would be a good president. CBS's "Face The Nation" host Margaret Brennan asked Gates if he stood by a statement from his memoir that Biden has "been wrong on nearly every major foreign policy and national security issue over the past four decades." "I think I stand by that statement," Gates said. <blockquote>MARGARET BRENNAN: I was rereading your memoir before we sat down to talk and you said in your memoir, Joe Biden is impossible not to like. Quote: "He's a man of integrity, incapable of hiding what he really thinks, and one of those rare people you know you could turn to for help in a personal crisis. Still, I think he's been wrong on nearly every major foreign policy and national security issue over the past four decades." Would he be an effective commander-in-chief? ROBERT GATES: I-- I don't know. I don't know. I-- I think I stand by that statement. He and I agreed on some key issues in the Obama administration. We disagreed significantly on Afghanistan and some other issues. I think that the vice president had some issues with the military. So how he would get along with the senior military, and what that relationship would be, I just-- I think, it-- it would depend on the personalities at the time. MARGARET BRENNAN: He's a peer of yours. Does that mean you're older? ROBERT GATES: Yes. MARGARET BRENNAN: You think he's right for this moment? ROBERT GATES: I think I'm pretty busy and pretty active but I think-- I think having a President who is somebody our age or older, in the case of Senator Sanders, is- I think it's problematic. I think that you don't have the kind of energy that I think is required to be President. I think-- I'm not sure you have the intellectual acuity that you might have had in your sixties. So, I mean it's just a personal view. For me, the thought of taking on those responsibilities at this point in my life would be pretty daunting.</blockquote> Watch the full interview: <iframe width="640" height="330" src="https://www.youtube.com/embed/aUWvITlpKd4" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>