For interests that are vital to the U.S. - that is, essential for our survival and wellbeing - the U.S. should be prepared to use military force - including unilaterally, if necessary.

There are two great tragedies in life: one is to fail to achieve one's grandest ambitions, and the other one is to succeed.

The fact that there are now many entities that may have some loose affiliation with a former core Al Qaeda - or who have decided to fashion themselves as an affiliate or follower in the Al Qaeda jihadist tradition - as well as groups that are just inspired by the concept that they could also be the perpetrators of mass killing, means that there is a spectrum of threats.

The absence of a focal enemy, which is what the Cold War had provided; the complexity of the developments that are occurring that mean that the world is just extremely complicated - lots of different and competing stories and strands; the continuing reality of megaterrorism; and the dysfunctionality of our politics that has neglected the foundations of the U.S. role in the world; have altogether left us somewhat confused.

The best simpleminded test of expertise in a particular area is an ability to win money in a series of bets on future occurrences in that area.

And I hope that we can learn the lessons of the past in looking at the current challenge that China poses to a ruling America.

Terrorism is really the only existential threat to America as we know it - as a free country that plays a leading role in the world.