American democratic socialists like Sanders aren't far left, and are really more social democrats than “literal socialists”. (Sure, DSA is part of international socialist fora, but so is the UK Labour Party, and no one sane is calling Labour “far left” either.)
Someone, therefore, from the moderate left getting a sizable minority of votes within the left-most party of a two-party system where the most votes in that party went to a center-right neoliberal is not evidence of the far left having much (or any) influence, especially when it's the best anyone not from the center-right has done in that party for at least a quarter century.
"These days, the American dream is more apt to be realized in South America, in places such as Ecuador, Venezuela and Argentina, where incomes are actually more equal today than they are in the land of Horatio Alger. Who's the banana republic now?"
Would you describe Venezuelan regime as center-left social democrat?
Who's the banana republic now? Indeed, the irony would be amusing if only this failure did not leave millions and millions of people with no money, no food and no hope.
If he became president and succeeded at first he might have been widely celebrated, as comrade Chavez was. Then he would have likely won the re-election in a landslide that dwarfed Reagan's victory and implemented policies further to the left.
And then a decade in the future (might even be more than that, US is resilient) it would have blown up in everyone's faces, just as it did in Venezuela.
The general public has a short attention span, it seldom thinks of what would happen 10-15 years down the road.
A literal socialist reaching 43.1% of votes not influential enough?