美國總統歐巴馬上任已達兩年，其對歐洲戰略進行大幅度調整，並與過去小布希政府時期的戰略呈現明顯差異。由於美國為典型的總統制國家，總統擁有對外政策的最高主導權，研究領導人認知因素成為分析美國對外政策的重要途徑。本文期望透過理論與政策的結合，有助於正確解讀歐巴馬與小布希政府在歐洲戰略上的思維與選擇，並做為觀察美國外交政策未來走向的重要依據。因此，本文研究重點為比較歐巴馬與小布希對外戰略思維之差異，且在此思維下，其在歐洲戰略的選擇上出現了何種轉變？未來大西洋兩岸關係又將如何發展？為回答上述研究問題，本文將採取新古典現實主義的研究途徑，進一步結合「權力」與「觀念」兩項要素深入檢視，據以辨析當前美國對歐洲戰略的思維與選擇。

U.S. has adjusted its strategy toward Europe which is different from
Bush administration since Obama taking office. Provided its presidential
system, U.S. president is given overwhelmingly right to direct foreign
decision-making process and leader’s cognition becomes the vital factor in
analyzing U.S. foreign policy. Being the moment between two presidents, we
can combine theory and practice to correctly explain the two
administration’s strategic thinking and choice toward Europe, so as to find clues observing the development of U.S. foreign policy. This article aims to focus following questions: What’s the different strategic thinking between Obama and Bush?Why does it affect their strategic choice? How would Trans-Atlantic relations develop? To answer these questions, it will adapt neo-classical realism to be approach which combines both power and idea in analyzing.