The United States (US) - the second largest greenhouse gases (GHGs) emitter in the world – has recently pledged a reduction of net GHGs emissions by 26–28% below its 2005 level by 2025. How big is the challenge for the country to achieve this target in terms of its present emissions profile, recent historical trends and the contributions to those trends from key proximate factors contributing to emissions? In this paper we make quantitative judgement of the challenge by using decomposition analysis. Based on the analysis and the contributions of the key drivers of energy-related CO2 emissions in the recent past, it appears that it will be quite a challenging task for the government to achieve the recently announced 2025 target. More specifically, to achieve it, the combined average annual mitigating contribution from energy efficiency, carbon intensity of energy improvements and continued structural change in the US economy away from emissions-intensive activities will need to be at least 33% higher, and depending on the extent of continued structural change in the US economy in the future, may even need to be as much as 42% higher than was apparently the case during the 2000 – 12 period.