To truly grasp what constitutes a horrible deed it's best to look to the past. When you can wholly ascertain cause and effect you get a much clearer idea on what goes against your particular political ideals, and what is decidedly bad.
For that reason we're completely ignoring any action from Jimmy Carter to the Current President because we need the instrument of time to understand what impacts were made that can be considered terrible.
The worst thing about looking into the past and finding dreadful actions from presidents (or indeed ANY world leader) is that nobody comes off as innocent. Sometimes when you hold a position of extreme power and have the ability to influence a numerous amount lives, horrible decisions will be made.
Every president has done something horrible, it comes with the job. Even William Henry Harrison who decided to show off how tough he was by giving a two hour speech in February without a coat. He died a month later by the way... didn't impact a lot of people but it was pretty stupid.
The actions we discuss are not always of equal quanitities of evil, at least one is just funny, but they are certainly the acts of jerks.
This is going to be a dark one, sorry.