Brien McMahon was born James O’Brien McMahon in Norwalk, Connecticut, in 1903, graduated from Fordham in 1924 and Yale Law School in 1927, and changed his name the year he joined the bar. After serving as a local judge he joined the Justice Department in 1933 under Attorney General Homer Cummings and was running its criminal division by 1935, prosecuting associates of Baby Face Nelson and the lawyer who had harbored John Dillinger. His prosecution of Harlan County coal operators for denying miners their union rights ended in a mistrial, but it made his name. In 1944 he won a U.S. Senate seat from Connecticut, beating isolationist incumbent John A. Danaher.

Months later the Trinity test changed his career. Named chairman of the Senate’s Special Committee on Atomic Energy, he offered his own bill against the military-backed May-Johnson bill and framed the fight as civilian versus military control. Truman signed the Atomic Energy Act on August 1, 1946, and McMahon became the first chairman of the Joint Committee on Atomic Energy. After the Soviet test in 1949 he became a leading advocate of the hydrogen bomb. He entered the 1952 presidential race, fell ill with lung cancer, and died on July 28, 1952, at 48.

• He called the atomic bomb the most important thing in history since the birth of Jesus Christ.
• He dismissed ethical objections to the H-bomb by comparing it to the firebombing of Hamburg and Tokyo.
• His 1952 slogan was The Man Is McMahon, and he also proposed sending young Americans abroad in an early version of the Peace Corps idea.
• From his sickbed he promised that as president he would order thousands of hydrogen bombs, and Connecticut still cast its 16 convention votes for him.
• A 1962 stamp honored his work on peaceful atomic energy, and he appears in the 1982 documentary The Atomic Cafe.