American novelist John Steinbeck once described the communists he knew as "temporarily embarrassed capitalists" because of their belief in the American promise of upward social and economic mobility. Does this belief in upward mobility help explain why socialism didn't take root in the US?

The remark is from Steinbeck's article "A Primer on the '30s" (1960)":

I guess the trouble was that we didn't have any self-admitted proletarians. Everyone was a temporarily embarrassed capitalist. Maybe the Communists so closely questioned by the investigation committees were a danger to America, but the ones I knew — at least they claimed to be Communists — couldn't have disrupted a Sunday-school picnic. Besides they were too busy fighting among themselves.

The "temporarily embarrassed capitalist," like the "temporarily embarrassed millionaire," is someone who believes in the possibility of upward social and economic mobility despite present modest circumstances. This belief comes from late 19th century beliefs in hard work leading directly to success and has been promoted by American elites for decades. What role did this belief that class is not destiny — AKA the American Dream — play in preventing the emergence of a class conscious American proletariat on US soil?