Some facts

Until 2006 U.S. was the largest carbon dioxide emitter. After 2006 was overcome by China.
During George W. Bush presidency it was claimed that signing Kyoto protocol will cost US economy $400B and 4.9M jobs.
US GHG Emissions:

To ratify an international treaty 67 senator of 100 votes in favor are required.
Waxman-Markey bill plans to reduce American greenhouse gas emissions to 17% below 2005 levels by 2020, and to 83% below 2005 levels by 2050. 25% of the nations energy should be produced from the renewable sources by 2025.
Negotiation team in Copenhagen was free to utilize the reduction goals in Waxman-Markey.
One of the major complaints of US in case of Kyoto Protocol and LCA are allowances for some developing countries such as China and India.

Mechanics within United States of America

US