Politically active, Sam Johnson served five terms in the Texas legislature as a Democrat. He is remembered for attacking the Ku Klux Klan on the floor of the Texas legislature during a time when many of his colleagues were Klan sympathizers (an event famously referred to by his son). He also was instrumental in the legislation that enabled the state of Texas to acquire the Alamo property in San Antonio, enabling that monument to be preserved as an important part of American history.