Perhaps Denman’s greatest historical contributions to the court were his consequential rulings on civil rights issues. In May 1943, Denman and his fellow judges ruled on the case of Korematsu v. United States and Endo v. United States—two cases challenging the government’s decision to incarcerate Japanese Americans during World War II. Denman at times clashed with his colleagues; when his colleagues chose to send an earlier case, Hirabayashi v. United States, to the Supreme Court instead of issuing a ruling, Denman declared it to be the “deportation of 70,000 of our citizens without hearing.”
In the case of Korematsu, Denman accused his colleagues, who upheld Fred Korematsu’s conviction, of again ignoring the due process issue at the heart of the case. When Mitsuye Endo’s case came forward as another challenge to the incarceration policy, Denman directly assisted Endo’s attorney James Purcell with certifying the case to the Supreme Court. In the end, the Supreme Court upheld the legality of the incarceration in Korematsu’s case. Its ruling in Endo’s case, however, had the immediate effect of ending the policy by allowing Japanese Americans to return to the West Coast.
In the postwar period, the judges on the Ninth Circuit tackled desegregation on the West Coast. Following the end of Japanese American incarceration, Denman and several judges ruled in favor of a set of Japanese American plaintiffs who petitioned to regain their citizenship. In April 1947, the judges of the Ninth Circuit ruled in Westminster v. Mendez that California schools could not target Mexican American students for segregation. Although Mexican Americans at the time were labeled as white and the parties in the case stipulated that racial discrimination was not at issue, the ruling in Westminster v. Mendez was among the first desegregation cases of the civil rights era.