Frustrated by Johnson's actions, Congress proposed the Fourteenth Amendment to the states, and the amendment was ratified in 1868. As the conflict between the branches of government grew, Congress passed the Tenure of Office Act, restricting Johnson's ability to fire Cabinet officials. When he persisted in trying to dismiss Secretary of War Edwin Stanton, he was impeached by the House of Representatives, making him the first U.S. president to be impeached. Johnson narrowly avoided conviction in the Senate and removal from office, but he exercised little power in his last year in office. In foreign policy, Johnson presided over the purchase of Alaska, and his presidency saw the end of the French intervention in Mexico. Having broken with Republicans, and failing to establish his own party under the National Union banner, Johnson sought the 1868 Democratic presidential nomination, but it went to Horatio Seymour instead. Seymour's defeat by Grant in the 1868 presidential election left Northern Republicans firmly in control of Reconstruction.