Complex sentence: Other members, such as J.T. "Jack" Murphy, were influential in the Sheffield Workers Committee and gradually abandoned the DeLeonist strategy of creating dual unions, taking the position of working within existing unions to win them to their ideas.
Split into simpler sentences: Other members, such as J.T. "Jack" Murphy, were influential in the Sheffield Workers Committee. They abandoned their syndicalist strategy of creating dual unions, and took up the position of working within existing unions to win them to their ideas.