I think that one of our most difficult international challenges is clearly climate change and making sure that the Paris agreement goes forward. While I think the international community understands that President Trump is not taking the same position as President Obama.

Climate change is the greatest threat of our time.

When consumers do not take full advantage of efficiency gains, it is because they are weighing other factors that influence their decision making. When the federal government arbitrarily places one of those factors over others, it makes consumers worse off.

I definitely challenge people. But hopefully, I am working harder than anybody else, and so people won't resent the fact that I want them to work hard, as well.

Greenhouse gas pollution, through its contribution to global climate change, presents a significant threat to Americans health and to the environment upon which our economy and security depends.

We need an international solution to the challenge of climate change, there's no question about it. But the real key is, can you actually get that - or get that solution - without the US' involvement? Can you not lead domestically, and expect the rest of the world will take action... the US needs to lead, we need to be out there.

States with tremendous oil and natural gas reserves have the most to gain economically from proper regulation.