I can't imagine that I would be asked that by the president-elect [Donald Trump], or then-president [Barack Obama]. But it's - I'm very clear. I voted for the change that put the Army Field Manual in place as a member of Congress. I understand that law very, very quickly and am also deeply aware that any changes to that will come through Congress and the president.

Our strategy right now is to accelerate the campaign against ISIS. It is a threat to all civilized nations.

Since 9/11 we've been engaged in wars around the world, and General [James] Mattis has been a leading battlefield commander in many of those theaters, including in the April 2004 siege of Fallujah, where the US Marines killed so many people that the municipal soccer stadium in the city had to be turned into a graveyard for the dead.

Nothing keeps me awake at night. I keep other people awake at night.

We do not draw red lines unless we intend to carry them out. We have made very clear that we are willing to work with China, and we believe China has tried to be helpful.

I just hope we can find our way back to engaging with one another, arguing strongly with one another, and then going down and having a root beer together or something and - and having a good laugh about it as we work together for the best interests of the next generation of Americans who are going to inherit this country.

I think as we look at this problem of ISIS, it's more than just an army. It's also a fight about ideas. And we have got to dry up their recruiting. We have got to dry up their fundraising. The way we intend to do it is to humiliate them, to divorce them from any nation giving them protection, and humiliating their message of hatred, of violence. Anyone who kills women and children is not devout. They have - they cannot dress themselves up in false religious garb and say that somehow this message has dignity.