This saying has been credited in turn to American broadcast journalist Edward R. Murrow, and French political economist Bertrand de Jouvenel. 

Fifty-odd years later, American syndicated columnist Andrew Napolitano titled his book Constitutional Chaos: The Constitution in Exile: A Nation of Sheep.

And, it was popularized by the title of a 1961 book about United States foreign policy by William Lederer: "Nation of sheep, ruled by wolves, owned by pigs".

In all these writings, the term "sheep" means submissive to authority and persuasion by others.

In just over 2 years, the flock went from imaginary BLAHS to bona fide SADS. 

And, I'm afraid, the whole situation is going to get sadser and sadser. In fact, there'll be plenty more sads going around soon and you can take your pick from the ever-growing approved list of causes: 

Covaids
Putin, Trump & China
Non-progressive conspiracy theorists:
Anti-vaxxers
Anti-abortionists
Anti-paeds
Transphobes
Meat eaters
Gun owners
Space aliens
Weed … and…
Cow farts and Sheep burps!
There's no discussion with the woke police. I mean, it's a SADS world where we have to debate "what is a woman", and "where are the men"?