In the 1930s, Ida Tarbell investigated the question of whether or not Marx and Lincoln corresponded. I think the WaPo author's use of the phrase "exchanged letters" implies that both men wrote each other personally. To date, no evidence has ever been found that they did. Here is the correspondence from Tarbell's papers. Of particular interest is the correspondence between Tarbell and Daniel Hoan, the socialist mayor of Milwaukee (fun fact: Milwaukee had three Socialist mayors. One, Emil Seidel, had a fledgling poet as his secretary by the name of Carl Sandburg).
https://dspace.allegheny.edu/handle/1045...one&page=1
Here's the link to the WaPo article, although I'm not sure if you'll be able to read it. Overall, while not completely accurate historically, I thought its tone was balanced.
https://www.washingtonpost.com/history/2...0b8c6915d6
Best
Rob
Not a Socialist, But a Marxist?
