Which of the following early twentieth-century presidents is most closely associated with environmental conservation?

William McKinley, the 25th president, is not primarily associated with environmental conservation efforts. His administration focused more on economic issues and foreign policy rather than on the establishment of conservation measures or the protection of natural resources, which became prominent under Roosevelt.

William Howard Taft, while he continued some of Roosevelt's conservation policies, is not primarily remembered for his contributions to the environmental movement. His presidency saw less emphasis on conservation compared to Roosevelt, and he faced criticism for actions perceived as favoring business interests over environmental protection.

Woodrow Wilson's presidency focused on progressive reforms and international affairs, and while he acknowledged the importance of conservation, he did not take significant action compared to Roosevelt. His administration did not prioritize environmental conservation to the same extent, making him less associated with this movement.