A contemporary of J. P. Morgan and a close business associate and friend of Jacob Schiff of Kuhn, Loeb & Co., Fleming was widely known and respected in financial circles on both sides of the Atlantic. He was one of the shrewdest investors of his generation and an acknowledged expert in the financing of American railroads. One of his less successful ventures was the 1908 takeover of the bankrupt works of Algoma Steel in Sault Ste. Marie, Ontario, but he had the foresight to associate with the project James Hamet Dunn, who would come to control the works from 1935.