What is the importance of the Gelman telegram in the novel, Advise and Consent?

The Gelman telegram is received by Senator Arly Richardson as the hearings on Leffingwell’s confirmation begin. The Gelman telegram reveals that Leffingwell spent time in a Communist cell dedicated to forcing Communism on America. The telegram is seized upon by Cooley and others as more evidence that Leffingwell is unfit to be Secretary of State. The telegram ultimately leads to the tracking down of Gelman and to Gelman’s personal appearance in the hearings as a witness.