America historically has been a drinking culture. The presidency is a stressful job. It's not surprising, then, that some presidents have had reputations for tippling.
Ulysses Grant brought his reputation to the White House. He drank himself out of the army after the war with Mexico. During the Civil War he went on a couple of benders between battles. Though his boozing never impaired his performance as president, he couldn't shake the reputation.
Richard Nixon's relationship with liquor might have been partly strategic. As the Watergate investigation was closing in on him during the autumn of 1973, Egypt attacked Israel. The Israelis had the worst of the initial fighting. Nixon wanted to warn the Soviets away from the conflict, lest the Middle East become an open battleground in the Cold War. He was drinking heavily during this period, and his impaired condition lent credibility to his “madman theory” of diplomacy, by which his drunken unpredictability would have a deterrent effect on Soviet adventurism. The Kremlin presumably would have to allow for the possibility that he was crazy enough, or drunk enough, to use nuclear weapons upon even modest provocation.
By the time Grant left office after two terms, and following a triumphal journey around the world during which he met with numerous heads of state, his drinking was forgiven if not forgotten. He might well have been the most popular man on earth in the late 1870s. Nixon's drinking didn't drive him from office. It was the lying.
For Andrew Johnson, by contrast, drinking was a presidency killer. To be fair to the liquor, Johnson's presidency faced troubles enough that a teetotaler might not have survived them. More than most vice presidents, Johnson was never intended to be a president. Lincoln replaced his first-term vice president, Hannibal Hamlin of Maine, in 1864 to give credibility to his campaign on the ticket of the National Union party, rather than the Republicans. Johnson was a Democrat, a Tennessean and a Unionist. The Confederate majority in Confederate Tennessee despised him as a traitor, which recommended him to Lincoln. But Republicans distrusted him as from the wrong party and the wrong section.
Johnson felt the pressure as his inauguration as vice president in March 1865 approached. He turned to liquor to ease the stress. The result was that he was visibly drunk at the inauguration ceremony.
Lincoln was dismayed “I can never forget President Lincoln's face as he came into the Senate chamber while Johnson was delivering his incoherent harangue,” recalled a Washington regular. “Lincoln had been detained signing the bills that had just passed the old Congress, and could not witness the regular opening of the new Senate till the ceremonies had fairly commenced. He took his seat facing the brilliant and surprised audience, and heard all that took place with unutterable sorrow.”
Another observer, who happened to be sitting next to Lincoln in the Senate chamber, said, “During the painful ordeal, Mr. Lincoln's head dropped in the deepest humiliation.”
At this point Johnson's behavior was merely embarrassing. He had served his purpose by helping Lincoln get reelected. Lincoln had no intention of delegating any authority to him.
But six weeks later Lincoln was assassinated, and Johnson became president. All of a sudden his insobriety mattered.
It gave his opponents an easy opening for attack. Congress wanted to claw back power it had lost to the executive during Lincoln's presidency. Republicans wanted to retain the dominance they had enjoyed during the war as a result of Southern — mostly Democratic — secession. Had Lincoln lived, even he would have faced a tussle. Johnson, without Lincoln's popularity and credibility, had things ten times worse.
There's no indication that Johnson's drinking impaired his judgment in making decisions. But it gravely impaired his ability to put those decisions into effect. His rivals for control of Reconstruction merely had to throw his performance at the inauguration back in his face.
They did just that when he undertook a speaking tour — a “swing around the circle" of the eastern half of the country — to promote his vision for the renormalization of national politics. Johnson lacked formal education, and he spoke in the vernacular of the working class of the upper South. His style was effective in person, but his words didn't translate well to the printed page, which is how most Americans encountered his speeches. He was easily mocked, and the mocking included insinuations that he must have been drunk.
He never had a chance. Congressional Republicans set an impeachment trap, a law forbidding the president to fire members of his cabinet. Johnson took the bait and was brought to trial before the Senate, where by a single vote he avoided conviction and removal from office.
Yet his influence was at an end. Congress completed its takeover of Reconstruction and Johnson served out his term as the lamest of lame ducks.
Being a good president is hard. You have to make good decisions, and you have to make a good impression. Johnson's decisions weren't as bad as his critics claimed, but the impression he made was so damaging his decisions didn't matter.
He was drinking on Inauguration Day because he was suffering from some malady. He wasn’t actually a drunk. He apparently tried to not even attend the inauguration because of it.
I think there is more to it than that. Johnson aided the old Southern leadership class that supported the Confederacy regain power through his wholesale pardons. Southern promptly instituted the black codes which placed southern blacks in a distinctly inferior status. He vetoed the Civil Rights Act of 1866. The conflict with Congress over the status of former slaves was the central issue of Reconstruction. Congressional Republicans may have acted “unconstitutionally”, but the alternative was to allow white Southerners to win in peace what they could not in war. Eventually, however, they did, as Jim Crow laws, disenfranchisement, convict leasing, and other policies undermined the gains made during Reconstruction.