Andrew Johnson was President Lincoln's Vice President during his short lived (literally) second term, and the 17th President of the United States following Abraham Lincoln's assassination at the hands of Booth. He is widely considered to have been one of the absolute worst president's in American history and has the dubious distinction of being the first and only president to ever have been impeached by Congress (not even Nixon was impeached), and to have given an inauguration speech when sworn in as Vice President which is widely recognized as one of the worst speeches in American history. It was rambling, incoherent and probably the result of public drunkenness on the part of the Vice President.
A slave owning tailor and politician from the Confederate state of Tennessee, Johnson nevertheless supported the Union. When war came he served the Federal government in various capacities and was eventually appointed by Lincoln to be military governor of the occupied parts of Tennessee which had been retaken by Union forces. He apparently did a creditable job, successfully managed the difficult defence of Nashville against Confederate raids and counter attack.
These successes convinced Lincoln to add him as his running mate for his second presidential election campaign, in the hopes that having a southerner on the ticket would help with national reconciliation. Political cartoons of the time emphasized Johnson's trade as a tailor and Lincoln's experience as a rail splitter, depicting the two men as stitching and repairing the Union. The Lincoln-Johnson ticket easily won re-election.
Johnson had been in office as Vice President for only six weeks, and in seclusion in order to hide from the public ridicule directed at him for his drunken and incoherent inauguration speech, when President Lincoln was assassinated, and this under qualified little man found himself having to fill very big shoes, when he became the next President of the United States. He proved singularly unfit for the job.
Johnson's views regarding Reconstruction following the Civil War placed him in constant conflict with Congress, which led to his impeachment when he fired the popular Secretary of War, William Stanton. He avoided being convicted by only one vote.
During and after the Wsr, the slave owning Johnson did not support emancipation for African Americans and he opposed the 14th Amendment which granted citizenship to former slaves. He even convinced President Lincoln to exempt Tennessee from the application of the Emancipation Proclamation, which freed the slaves in Confederate territory.
Johnson did eventually come out against slavery, but not because he recognized it inherent moral evil. Instead, he reasoned that since the institution of slavery had attempted to destroy the Union, the Union had the right to destroy slavery. It was a pragmatic solution to his views, which make him out to be clearly an unworthy heir to Lincoln, the great Emancipator. His position on slavery is also somewhat ironic given that as a youth, he had run away from his master after being hired on as an indentured apprentice; one would think that he could at least sympathize with the misfortune of slaves.
After narrowly escaping being convicted by the Senate, Johnson did not seek re-election. After his term as president, he sought a sort of political redemption by running for and being elected a Senator from Tennessee. He is the only former President to ever have been elected senator after his term in the Oval Office.