The question implies you will have to divide the paper in 2 parts:
The first part will have to answer why did Truman use the atomic bomb or if you prefer this part of the assignment will focus on the internal struggles regarding the use of the new weapon.
The second part will have to answer the broader aspect of American Foreign Policy and the priorities of the US government prior to the use of the bomb. The second part should focus on the broader aspect such as What the United States was facing before the detonation on Hiroshima then Nagasaki in Europe for example? What were the challenges for Washington at that period of time? DO NOT FORGET: DO NOT GO INTO MANY DIRECTIONS AND DO NOT GO AFTER HIROSHIMA AND NAGASAKI
Your paper is still limited in terms of pages: 4 double spaced so do not forget to go to the point and be concise.
Use this book as a source: J Samuel Walker: “Prompt and Utter Destruction: Truman and the Use of Atomic Bombs Against Japan”, however, do not use block quotations and use FOOTNOTES to cite the information.