Which president signed the UCMJ into law?

The Uniform Code of Military Justice (UCMJ) was signed into law by President Harry S. Truman on May 5, 1950. The UCMJ established a comprehensive legal framework for the governance of the United States military, integrating various military regulations and establishing a unified set of legal provisions applicable to all members of the armed forces. Truman's administration was pivotal in reforming military law, and the enactment of the UCMJ provided a necessary update to the military justice system, ensuring that it was fair, efficient, and consistent across branches. The UCMJ remains in effect today, highlighting its significance in shaping military discipline and justice.

The other options do not fit as the UCMJ was not signed into law during their presidencies.