We [the United States] are the world's only superpower right now, so everyone notices every bit of what we do or don't do.

A lot of it was, you know, you look for moments where, for instance, we were dependent on Abraham Lincoln making sure that the slaves were freed or John Kennedy bringing civil rights, or the first one I wrote about, George Washington trying to stop the British from invading and ending this country before it even began. Those were turning points where, if you had not had a president stepping up to the plate, if there wasn't a story like that, we would not be here.

You have had presidential candidates over the last 30 years who would have had a very hard time getting nominated under the old system. One example is John Kennedy.

First of all, there's no mention of political parties in the Constitution, so you begin American history with not only no political conventions but also no parties.

We cannot be spun, or at least we'd like to think that we cannot be. And the presidents who are trying to - too overtly to try to say, here is what you historians and what you later Americans should think of my presidency, 30 or 40 years later, they look silly.

The original thing that fascinated me most was why we expect leaders, and especially presidents, at times to destroy themselves - and that's a sign of being a good leader or a good president. We usually don't expect that of almost anyone else in any profession, in particular, in public life.

I'm defining [presidential courage] pretty narrowly. It's not only taking a big political risk but it's also the risk that in the hindsight of history, people think it's wise.