Historical rankings of presidents of the United States

Historians (and sometimes political scientists) are surveyed and asked to give presidents of the United States number ratings on their overall performance or on different aspects of their leadership.
Several different factors are considered in deciding what makes one a good or bad president. These include their character, their vision for the country, their relations with congress, their relations with foreign leaders (diplomacy), how they managed the economy, how they managed the military, and their overall political skill.
To make sure the rankings are fair, many surveys equally balance the opinions of Democrats and Republicans.
It is sometimes difficult to accurately rank a president because all of the presidents faced completely different challenges.
Historical opinions of U.S. presidents may change over time. For example, Harry S. Truman had very low approval ratings after he left office, but many historians now consider him among some the greatest presidents.
General findings.
Highly ranked.
The following presidents are usually ranked highly:
Mixed ratings.
Some presidents have mixed ratings. For example, Andrew Jackson stood for the common man, but was criticized for implementing the Trail of Tears. Ulysses S. Grant is thought to be a bad leader since he had corruption surrounding him, but he helped African-Americans to have more rights in the Reconstruction Era.
Examples of presidents with mixed opinions include: