My experience is that the director of the FBI is particularly important to just how aggressive an investigation will be into an issue. And once you remove James Comey, it creates a vacuum at the top. And the fundamental issue will be whether or not there is support at the highest levels within the FBI to continue to conduct that investigation. That's going to be the question mark.

After every major conflict - World War I, World War II, Korea, Vietnam, the fall of the Soviet Union - what happened was that we ultimately hollowed out the force, largely by doing deep across-the-board cuts.

The reason we've always had a civilian in that job [Secretary of Defence] is because we really believe that it is policymakers who ought to control the military and not have the military control the military.

The reality is that the United States military alone cannot be all things to all nations. We will sharpen the application of our resources, better deploy our forces in the world and share our burdens more and more effectively with our partners. And frankly, all our allies need to do the same.

Go forward, knowing that you are greater than the challenges of your time.

The one thing that I remember from all of my intelligence briefings and my dealings with the Russians is that when you deal with the Russians, you have to deal with them from strength, not from weakness.

I suddenly realized at the CIA that I had to make life-and-death decisions about people.