Truman responded that the U.S. would take “whatever steps were necessary” to contain communist expansion in Korea. A reporter asked “Will that include the atomic bomb?” to which Truman replied, “That includes every weapon that we have.” In 1945, Truman authorized the use of two atomic bombs to end the war with Japan.
https://www.history.com/this-day-in-history/truman-refuses-to-rule-out-atomic-weapons