This letter was written by Trotsky in English
December 20, 1939
Dear Comrade Shachtman,
I am sending you a copy of my last article. You will see from my polemics that I consider the divergences as of decisive character. I believe that you are on the wrong side of the barricades, my dear friend. By your position you give courage to all the petty-bourgeois and anti-Marxist elements to fight our doctrine, our program, and our tradition. I don’t hope to convince you with these lines, but I do express the prognosis that if you refuse now to find a way towards collaboration with the Marxist wing against the petty-bourgeois revisionists, you will inevitably deplore for years and years the greatest error of your life.
If I had the possibility I would immediately take an airplane to New York City in order to discuss with you for 48 or 72 hours uninterruptedly. I regret very much that you don’t feel in this situation the need to come here to discuss the questions with me. Or do you? I should be happy. …
The article referred to is “A Petty-Bourgeois Opposition in the Socialist Workers Party.”