 In 1927, Gropper went on a tour of Soviet Russia along with the novelists Sinclair Lewis and Theodore Dreiser in celebration of the tenth anniversary of the Russian Revolution.During the second half of the 1930s, Gropper dedicated his art to the efforts to raise popular opposition to fascism in Europe.The lobby of the Freeport New York Post Office features two murals by Gropper installed in 1938 and titled "Air Mail" and "Suburban Post in Winter".