In 1917, Tobin defeated John B. Lennon in the race for treasurer of the AFL. Although membership in the AFL had risen to 2.371 million in 1917 from 2.072 million the year before, socialists and others in the federation felt that Lennon had not been sufficiently aggressive. Tobin, however, was forced to defend his previous actions, denounce pacifism, and declare his full support for the war effort. AFL president Samuel Gompers and Tobin quickly became close friends and supporters of one another. Tobin quickly became one of the inner circle of AFL vice presidents (which included Matthew Woll, John P. Frey and William Hutcheson). During the presidency of William Green, Tobin and the others largely controlled the AFL.