Foster moved to Washington, DC, under President Ulysses S. Grant, and had a summer home in Watertown, New York. As a reward for his political service after the Republican Party split in 1872 as a result of scandals and rampant corruption in Grant's first administration, which even reached Vice President Schuyler Colfax and had caused reformers to nominate Horace Greeley in futile opposition to Grant's second term, successive Republican Presidents Grant, Rutherford B. Hayes and James A. Garfield appointed Foster the U.S. Ambassador to Mexico (1873–1880), then to Russia (1880–1881). President Chester A. Arthur made Foster the United States Ambassador to Spain (1883–1885).