 Complete the following phrase:  In 1928 Stalin moved against his former allies, defeating Bukharin, Rykov and Tomsky at the April 1929 Plenary Meeting of the Central Committee and forcing Tomsky to resign from his position as leader of the trade union movement in May 1929. Tomsky was put in charge of the Soviet chemical industry, a position which he occupied until 1930. He was not re-elected to the Politburo after the 16th Communist Party Congress in July 1930, but remained a full member of the Central Committee until the 