In September 1948, at the Annual Meeting of the American Association for the Advancement of Science (AAAS), President Truman, with Condon sitting nearby on the dais, denounced Rep. Thomas and HUAC on the grounds that vital scientific research "may be made impossible by the creation of an atmosphere in which no man feels safe against the public airing of unfounded rumors, gossip and vilification". He called HUAC's activities "the most un-American thing we have to contend with today. It is the climate of a totalitarian country". Condon opposed any cooperation with Congressional attempts to identify security risks within the scientific community. In June 1949, in a sharply critical letter to Oppenheimer, who had provided information to HUAC about a colleague, he wrote: "I have lost a good deal of sleep trying to figure out how you could have talked this way about a man whom you have known for so long, and of whom you know so well what a good physicist and good citizen he is." In July 1949, he testified before a Senate subcommittee that was considering rules governing the operation of Senate committees. He criticized Thomas and the HUAC for holding closed hearings and then leaking information that denigrated his loyalty and that of other scientists. He said that the committee denied his and his colleagues' requests for public hearings so they could respond.