A member of the Republican Party, he was one of the most popular U.S. presidents to that point. After his death, a number of scandals—including Teapot Dome—came to light, as did his extramarital affair with Nan Britton; each eroded his popular regard. Harding is often rated as one of the worst presidents in historical rankings. Harding is often rated as one of the worst presidents in historical rankings. Harding appointed a number of well-regarded figures to his cabinet, including Andrew Mellon at Treasury, Herbert Hoover at the Department of Commerce, and Charles Evans Hughes at the State Department. A major foreign policy achievement came with the Washington Naval Conference of 1921–1922, in which the world's major naval powers agreed on a naval limitations program that lasted a decade. Harding released political prisoners who had been arrested for their opposition to World War I.