An aggressor nation or extremist group could gain control of critical switches and derail passenger trains, or trains loaded with lethal chemicals.

The area of climate change has a dramatic impact on national security.

Rising sea levels, severe draughts, the melting of the polar caps, the more frequent and devastating natural disasters all raise demand for humanitarian assistance and disaster relief.

We have throughout our history been tested when it comes to the institutions of our democracy. And thank God our forefathers were smart enough to establish a government of checks and balances to make sure that power cannot be centralized in any one branch of government. And those institutions have proven themselves.

China is a major power in the Pacific and I think we are dealing with some common threats in that region: the whole issue of Korea and the stability of Korea, the whole issue of nuclear proliferation, the whole issue of providing free access to our ships that are operating in that area.

I don't think there's any question that America is safer as a result of the bin Laden operation.

The potential for the next Pearl Harbor could very well be a cyber-attack.