Woodrow Wilson
From what I understand, his desire/desparation to get the league of nations going got him to agree to terms of the treaty of versailles which was incredibly punitive against Germany. This basically ensured that a "Hitler" was going to arise at some point, it was just a matter of when and what exact flavor. The treaty was incredibly harsh but just not enough actually stop Germany hitting back (as can be seen in WW2 20 years later). In reality they should either have dissolved Germany right there and made a diaspora of the German people at that point(or worse) or been Magnanimous in their victory so as to not create guaranteed future enemies.
I mean imagine if the USA had pulled a treaty of Versailles on Japan post WW2? Would we have had a WW3 another 20 years later? Instead they led the reconstruction and reformation of the country and secured it as an ally or at least non enemy. You need to either show mercy, or kill your enemy outright. A "country" is not something that you can leave humiliation like that festering in, a person may die or let something go.... eventually........, but people have children and they will carry on they agendas of their parents, they will wonder why they are being punished for something they didn't do.
It really bothers me to know that one person literally held the future of the entire @#$@$%@ world in their hands right their and they botched it that terribly. This was a United States @#$@%@ president for God' sake, especially at that time no one was in a position to tell us what to do, no one. And yet he caved, he was weak, he had a lack of character, conviction, moral fiber, the vision and fortitude to shape the world. It would have been so easy, but he let it crumble. We are still paying for his failures.
I could only hope to not be as bad as him if for some reason I ever ended up in that position, I can only hope to be better......
Also as mentioned by others all that actual, real, racist crap with Woodrow Wilson, which is not even comparable to "witch hunt tier" racism that I see today.