which nusery rhyme has the darkest meaning

Rock a bye baby

Clarification: I was NOT suggesting people vote for Trump... I was entering that as the nursery rhyme with the darkest meaning (and outcome).

Vote for Trump...

Ring around the rosie.

It's more of a song but...definitely Didn't Leave Nobody But The Baby, especially when you've seen O'Brother Where Art Thou.

London Bridge is falling down

Ring around the rosie was about the Plague