He was also a member of the Subcommittee on Internal Security. He was a strong supporter and friend of Joseph McCarthy and engaged in McCarthyism. Jenner and McCarthy were both part of "a core of isolationist Republicans in the Senate" along with Herman Welker of Idaho and George W. Malone of Nevada. In 1950, when McCarthy issued a report falsely accusing a number of State Department employees of being secret Communists (see Tydings Committee), Jenner supported him, claiming that the State Department had engaged in "the most scandalous and brazen whitewash of treasonable conspiracy in our history" and stating: "Considering the fact that we are now at war ... how can we get the Reds out of Korea if we cannot get them out of Washington?" When McCarthy was censured by the Senate in 1954, Jenner gave a speech suggesting that censure resolution "was initiated by the Communist conspiracy."