The fact that he genuinely hates white people, while other racist presidents have, for the most part, merely thought people of other races to be inferior, makes his racism particularly vile.
With that said, I do suspect that a few 20th century democrat presidents did actually hate blacks - Woodrow Wilson, Franklin Roosevelt and Lyndon Johnson in particular.
There are several questionable assumptions there, but start with the idea that people who "merely" think another race inferior are worse than those who have an animus or hostility against a different racial group.
Somebody's feeling that you are inferior may actually be stronger and more pernicious and harder to uproot than your "hatred" of them. I'm not saying that it always is, but it's certainly possible.