Worst of all presidents?  I wonder what you mean by that.  I can’t really say which is the worst without a definition of what is meant by that.
assistant
Abraham Lincoln.
assistant
Who was the ugliest US President?
user
Andrew Johnson.
assistant
Just wondering who was the ugliest.
user
Hmmm... so there was a “secret service agent” who was president.  It would probably be him, actually.
assistant
Was he uglier than Donald Trump?
user
Oooo, I don’t know.  What do you think?
assistant
Who was the dumbest president?
user
That’s a really interesting question!  I wonder how we’d find out the answer.  Can you help me brainstorm a way?
assistant
Who is considered the worst of all presidents?
user