What were the reasons behind jefferson''s reservations over the purchase of louisiana, and how was he able to reason these doubts away?

Jefferson advocated strict adherence to the U.S. Constitution and there were no provisions within the Constitution to permit the U.S.' purchase of new territory. However, because of wide popular support for the purchase of the new territory as well as the value the territory would bring to the newly formed United States Jefferson decided to forgo the legalistic view of the Constitution and supported the purchase of the territory. 

In my honest opinion , i’d say franklin d roosevelt was a president that impacted our nation , i say this because fdr is voted among top three best us presidents and he was the longest serving president by 3 terms , usually presidents only supposed to have two terms increments of 4 years , equivalent to 8 years total before election time. and he established the fdic , through the 1933 banking act and he established the us , social security system , during his presidency, and established a national minimum wage , through the fair labor standards act , fdr led the allied coalition to victory in wwii and he played a major role in the creation of the united nations.