This week I've travelled more than 15,000 miles from America to China to Burma to Australia. I have no idea what time it is right now.

Time is running out for Iran to address the international community's growing concerns about its nuclear program.

I don't want my generals or my defense secretary or my national-security team to ever feel deploying weapons to kill people as routine or abstract, even if the targets are bad people.

What we've seen at least since 1979 is Iran making constant, calculated decisions that allow it to preserve the regime, to expand their influence where they can, to be opportunistic, to create what they view as hedges against potential Israeli attack in the form of Hezbollah and other proxies in the region.

You have social media and the Internet and immigration and so, suddenly, cultures are clashing and people feel as if they're less familiar with the people around them. That causes social anxieties.

The American story has never been about things coming easy. It has been about rising to the moment when the moment is hard. About rejecting panicked division for purposeful unity. About seeing a mountaintop from the deepest valley. That is why we remember that some of the most famous words ever spoken by an American came from a president who took office in a time of turmoil: "The only thing we have to fear is fear itself.

The best education I received was working with people in the community on a grassroots basis. Because what it taught me was that ordinary people, when they are working together can do extraordinary things.