In 2009 the US House of Representatives passed legislation requiring reductions in greenhouse gas emissions by 18 percent over the coming decade. Later that year, President Obama went to Copenhagen to sign a treaty requiring reductions by 50 percent over a two-decade period. The President came back with nothing: no firm commitment to reduce emissions and only a vague target to hold global temperature rises to under 2 C. How does a President who has a 75-vote majority in the House and a 19-vote majority in the Senate who has pre-approval for a treaty reducing greenhouse gas production by 18...