"In the 1950s, Niebuhr described Senator Joseph McCarthy as a force of evil, not so much for attacking civil liberties, as for being ineffective in rooting out Communists and their sympathizers.[78] In 1953, he supported the execution of Julius and Ethel Rosenberg, saying, "Traitors are never ordinary criminals and the Rosenbergs are quite obviously fiercely loyal Communists ... Stealing atomic secrets is an unprecedented crime."
I don't know about the Marxist part:
"In the 1950s, Niebuhr described Senator Joseph McCarthy as a force of evil, not so much for attacking civil liberties, as for being ineffective in rooting out Communists and their sympathizers.[78] In 1953, he supported the execution of Julius and Ethel Rosenberg, saying, "Traitors are never ordinary criminals and the Rosenbergs are quite obviously fiercely loyal Communists ... Stealing atomic secrets is an unprecedented crime."
Where is this from?
Wikpedia. Source: Fox, Richard Wightman (1985). Reinhold Niebuhr: A Biography. San Francisco: Harper & Row (published 1987). ISBN 978-0-06-250343-5.