Take a listen to Arolo Guthrie's "1913 Massacre" on his Hobo's Lullaby Album. Copper boss gun thugs shout "fire" and start a panic in a union dance. They block the door so nobody can get out. Closer 73 children are smothered.
Check out the ending of "Ironweed" where thugs dispose of a hobo camp by beating the life out of them while they sleep with iron pipes and axe handles.
Or the slaughter in "Matewan" ...
Closer to home ...
My ex-father-in-law from my first marriage was a union man. Company thugs beat his friend to death in a bar in Dayton Ohio. He barely escaped with his life.
The point: By the mid-20th century, a fair percentage of America's working class were unionized. They had a long institutional memory of what it took to make it possible.
They had a healthy skepticism of what bosses, corporations, land speculators, con artists and big talkers were up to.
Which is to say, the USA had a left-wing contingent actually comprised of working people. They had meeting places, an in-group language, a shared history, a don't-fuck-with-us attitude, and a sense of solidarity.
This is not to paint a joy-happy picture of some idealized union utopia. I know the sins/crimes/flaws of unions as well as anybody. The point is that a network of left-leaning working class people existed in the first place.
Shit happened. Nixon rolled in with his "Southern Strategy" and a drumbeat of law and order. The Arabs cut off America's oil after the 1973 war in Israel. The economy went stinko for a variety of reasons. Iran grabbed the American embassy and made us look bad. Our rescue attempt went down in flames. Reagan stole Carter's debate prep book and rolled into the White House with promises of morning in America.
And, in 1981, Reagan gave the striking Paatco Union the shaft.
Without a unionized working class, the preponderance of left-wing Americans are college educated types. They don't hang out with the guys at the service station, the blah, the whatever. They don't speak the same language.
This creates the perception of a "liberal elite" trying to impose its vision of utopia on everybody else.