One hundred and fifty years ago today, on March 13, 1868, the U.S. Senate began the impeachment trial of President Andrew Johnson. A Tennessee Democrat who remained loyal to the Union during the Civil War, Johnson had been placed on Abraham Lincoln’s 1864 reelection ticket as the ultimate example of sectional reunion. During that campaign, the Republicans temporarily re-branded themselves the “Union Party,” and what better epitomized national union than a northern Republican and a southern Democrat running together? No one ever expected Andrew Johnson to become president—but no one expected John Wilkes Booth to murder Lincoln, either.

But Booth did exactly that, and on April 15, 1865, Johnson became president. Since Congress was in recess until December, Johnson had a free hand in what he called “restoring” the former Confederate states to the Union.

Despite agreeing to be Lincoln’s running mate in 1864, Andrew Johnson was no Republican. At heart, he was an old Jacksonian Democrat who hated the rich planters who treated folks like him with disdain and also loathed his black neighbors. While Lincoln viewed the Republican Party and the national government as tools to expand equality for all, Johnson wanted to control Reconstruction policy in order to return power to southern Democrats like himself and maintain white supremacy. In summer 1865, he pardoned all but about 1,500 former Confederates. Then, when Congress reconvened in December, he announced that Reconstruction was over and northern congressmen must readmit the southern states, despite the fact that their legislatures had passed laws, collectively known as Black Codes, that essentially reinstated a form of racial slavery. The Black Codes prevented African Americans from congregating or owning guns and required them to sign yearlong work contracts. Failure to obey the laws could lead to whipping, jail, or fines, which could be paid by a third party to whom the offender would then be bound until he could pay his debt—a system that looked mightily like slavery without the name.

Republicans refused to readmit southern states under these conditions, and in early 1866 tried to protect their black allies in the South with two bills: one that permitted the Freedmen’s Bureau to establish federal courts in the South, and another that made African Americans citizens and gave them equal protection under the law (both later encoded in the Fourteenth Amendment). Johnson vetoed both of these bills on the grounds that they would be too expensive and they gave black men rights that the government had never given to white men. And then he dropped a bombshell. Congress, he wrote, could not legislate with the southern states unrepresented. By his reasoning, Republicans in Congress were operating illegally.

Republicans greeted this announcement with astonishment. After all, they were simply trying to protect the government’s victory over the southern rebels. They repassed their bills over his vetoes and prepared their own rules for the return of southern states to representation in the U.S. government. They embodied those rules in the Fourteenth Amendment, which made anyone born or naturalized in America a citizen entitled to due process of the laws, made many of the ex-Confederates Johnson had pardoned ineligible to vote, and made it illegal to repay Confederate debts, thus making it virtually impossible for secessionists again to raise money to rebel against the government. To regain seats in Congress, southern states had to ratify the Fourteenth Amendment.

This was quite a moderate set of requirements for reunification after a war that had cost 700,000 lives and more than $5 billion —there was no confiscation of land or call for executions, for example—but a furious Johnson told southern Democrats to ignore Congress. Democrats would sweep the 1866 midterm elections, he promised, and then his own program would go into effect. To win voters, in the summer of 1866, Johnson gave a series of speeches on his infamous “Swing around the Circle” on a loop through New York, Illinois, Missouri and back to Washington. To jeering crowds, he compared himself to the martyred Lincoln and to Jesus Christ. He also called Republican congressmen traitors and said that some of them should be hanged. Emboldened southern Democrats attacked African Americans in Memphis and New Orleans, killing more than 60 African Americans, 3 others, and destroying more than $100,000 in property. Horrified voters gave Republicans a two-thirds majority in Congress.

Congress set out to stop Johnson, but while his attempt to destroy Congress was certainly an attack on America, it was not clear how his actions were illegal. So Congress had to find a specific crime. In 1867, congressional Republicans passed the Tenure of Office Act (over another Johnson veto) specifically to protect Secretary of War Edwin Stanton, a Lincoln holdover who had raised Johnson’s ire by working with Congress. The Act required the president to seek the advice and consent of the Senate before dismissing any cabinet member or federal official whose initial appointment had required Senate approval. Five weeks later, Johnson fired Stanton and, after briefly making General Ulysses S. Grant the acting Secretary of War, appointed General Lorenzo Thomas to replace Stanton. When Thomas went to the War Department, he found Stanton barricaded in his office.

Spectator’s ticket to the first day of the Johnson impeachment trial-March 13, 1868. (Library of Congress)

Republicans pounced. “Sir,” cried Representative William D. Kelley of Pennsylvania, “the bloody and untilled fields of the ten unreconstructed states, the unsheeted ghosts of the two thousand murdered negroes in Texas, cry, if the dead ever evoke vengeance, for the punishment of Andrew Johnson.” Two days later, by a vote of 126 to 47, the House of Representatives voted to impeach President Johnson for high crimes and misdemeanors. The House adopted eleven articles of impeachment related to Johnson’s violation of the Tenure of Office Act, but the heart of its complaint was tucked into the tenth article, which accused the President of “making three speeches with intent to sow disrespect for the Congress” among the American public.

Johnson’s trial in the Senate, overseen by Chief Justice Salmon P. Chase, lasted about six weeks. Though most Americans reviled Johnson, moderates feared that removing him would obliterate the constitutional system of checks and balances, permitting future Congresses to claim presidential heads over policy disputes. The Senate needed a two-thirds majority—36 votes—to convict Johnson and remove him from office. On three different occasions, senators returned thirty-five votes of “guilty” and nineteen of “not guilty.” Johnson was therefore acquitted by a single vote.

By insisting on the importance of America’s legal process, the congressmen of the Reconstruction era guaranteed that the nation’s government would not crumble on their watch, even under the attacks of a rogue president. And while Andrew Johnson was not convicted, he was politically neutered. Though he had entertained delusions of being the Democratic nominee for president in 1868, he was so politically damaged that no one wanted anything to do with him. He handed the White House over to Republican Ulysses S. Grant in 1869, and today historians consistently rank him as one of the worst presidents in American history.