The two presidents with the strongest reputations for being hard drinkers are probably Franklin Pierce and Ulysses Grant. Both had been generals who had been to war and seen its horrors (Pierce in the Mexican War and Grant in both the Mexican War as a lieutenant and in the Civil War as a general.) Pierce had personal tragedies in his life, the most significant being the deaths of his infant children. After losing two children as infants, the Pierces doted on their youngest son Benny. On the way to his inauguration, the train that the Pierces were riding derailed and in the crash Benny was crushed and suffered a horrible death in view of his parents. Jane Pierce believed that God had taken their son so that her husband could concentrate on the presidency, and left Washington before the inauguration, never to return.
Pierce struggled with his drinking during his days as a senator, but managed periods of sobriety. He once managed to do so by joining the Temperance League of Concord, New Hampshire. As President, Pierce had many friends who had left their wives back in their home states. As author Cormac O'Brien puts it, Pierce and his friends in congress "loved to get together and act like frat boys." Alcoholism likely claimed Pierce's life, when be died in 1869 due to stomach inflammation.
Ulysses Grant is described as a binge drinker. Some of his worst drinking occurred after the Mexican War when Grant was posted in the Pacific northwest apart from his family. His drinking got so bad that his commanding officer asked for and received Grant's resignation. Grant's triggers seemed to be boredom and separation from his wife. During the siege of Vicksburg, General Grant was said to commandeer a riverboat for all-night drinking binges. Assistant Secretary of War Charles Dana said that General Grant would get "as stupidly drunk as the immoral nature of man would allow."
Fortunately for the nation, Grant's drinking subsided during his time in the white house. His wife Julia was able to maintain control of her husband, making sure that the nation was steered by sober hands.