Which American President Has Made The Most Impact On USA History?

When this question is being considered, George Washington certainly figures: as the first ever president, he inevitably set precedents that would affect the whole way the presidency operated and was viewed, so influencing all the presidents who came after him.  Franklin D Roosevelt was president for 12 years, a clear record (no-one else served more than eight years).  This, together with his leadership of the USA in World War II and his work combatting the economic Great Depression of the 1930s - notably his 'New Deal' - means he made a major impact on the nation's history.  However most people view Abraham Lincoln as having made the most impact on his country's history due to his role in keeping the Union together by leading the North to Civil War victory against the Southern states, who were looking to leave the Union over the North's desire to abolish slavery.  The subsequent abolition of slavery is also attributed in large part to Lincoln, adding to the huge impact he made on U.S history.  Lincoln was the first Republican president and held the office from 1861 till 1865, the same period in which the Civil War was fought.  He was assassinated in 1865.