Which, as history is so fond of pointing out, is never a good idea. Picking a Vice President not on merit but on ticket balancing always comes back to bite ya in the ass (and rarely is that ever a good thing. Maybe once in our history has it worked well to the nation's benefit).
I've railed against this before, in my talks about Vice Presidents being both a redundancy AND a headache in the worst of circumstances. What happened here - with Lincoln dying on the eve of victory over the Confederacy, and Johnson promoted to the Oval Office at the beginning of a serious Reconstruction moment - should always be used as Exhibit A on getting rid Veeps and replacing them with a more Senate-oriented office. It should certainly makes parties and Presidential candidates go with Best-Possible-Choice as Veep with regards to getting someone who complements (not contradicts, which is what most ticket-balancers are) the head of the ticket and the party.
Whereas Lincoln was "liberal" in the small-L sense - pro-government, for one thing - Andrew Johnson was more conservative. Whereas Lincoln showed a propensity for deal-making, compromising, and maneuverability, Johnson was upfront and bull-headed. Where Lincoln was Active-Positive, Johnson showed every trait of being Active-Negative.
That A-N trait was easy to spot: Johnson had a habit during his congressional career of making himself disliked and advocating for positions that were popular among the gentry - he supported direct election of Senators, which at the time was a radical anti-state party position - but not among the elites. As President he quickly developed an Uncompromising reputation, which at first the Republicans in Congress thought would mean Johnson being harsh towards the rebel South.
The problem was that the Northern Republicans mis-interpreted Johnson's hatred of the Southern political machinery. Johnson hated the oligarchs - the landed slave-owners - but not his fellow Southern whites that made up Johnson's voting base. Worse, Johnson sought to re-secure that power base by appealing to those Southern white voters... which meant Johnson wanted the Southern state governments back up and running and also meant Johnson didn't give a rat's ass about the newly freed Blacks.
Gotta read Eric Foner's Reconstruction, a review of this era, to get more understanding of the damage Johnson did to post-Civil War American history. Johnson during the post-war period vetoed against any federal efforts to improve freedmen rights. He openly campaigned against financial or educational aid, claiming it would make Blacks "indolent". He argued that aid to the Blacks meant punishing the Whites. Rather than see the benefits of having a newly emerged voting bloc - freed Blacks - as part of a voting base that would have included moderate Whites, Johnson decided to throw all in against Blacks... basically creating a campaign method the Deep South would utilize for another 100 years (and in some parts even longer).
His veto of the Civil Rights Act of 1866 was the break with the Republican Party that had brought him into the Union ticket. Congress overrode that veto: the first time a vetoed bill had been overridden (other veto overrides were negotiated into compromised deals). From then on they were in full opposition... and Johnson's mishandling of the political stage - his A-N view made him arrogant enough to think he had more support across the nation than he did - led to massive Republican gains in the midterms, creating an environment where a hostile President and hostile Congress were at political war.
That Johnson was impeached should not come as a surprise: when you have an A-N President - habitually conservative by nature - opposing a technically liberal Congress - the Radical Republicans of that era were Leftist (albeit pro-business: unions were not a vogue thing for liberals yet) rather than Far Right of this era - the urge to remove the A-N President is pretty high (and given how liberal/left have pro-government leanings, relying on government rules to fix a problem is a basic instinct). That Johnson really wasn't a Republican (echoes of Tyler) while Congress was made up of Republicans added to the likelihood. Problem was Johnson may have been a pain-in-the-ass and a g-ddamn racist, but he wasn't as corrupt as some of the other impeachable A-Ns tend to be. So Congress created a law they knew Johnson would break - the Tenure of Office Act - and basically dared him to break it.
Never dare an A-N President to do anything, because he will do it despite the trap. Using the moment to get rid of a Cabinet troublemaker - Secretary of War Stanton - Johnson fired a member of his administration without getting Congressional approval. Arguing that since the Senate had to approve Presidential nominees, the Republicans claimed they needed approval of firings as well, a right never spelled out in the Constitution. With their excuse in place, the House voted to impeach Johnson, the first impeachment vote to pass against a President. It then went to the Senate for what most Republicans saw as a fait accompli.
That Johnson survived the impeachment by one vote remains a major surprise in American history. What happened were a series of other factors: Johnson's lawyers were able to argue - rather correctly - that the Tenure of Office's wording meant that Johnson could not fire his own nominated Cabinet members, and since Stanton wasn't (he was held over from Lincoln's) the law did not apply; Johnson, facing his own political demise, finally offered up concessions to the moderate Republicans that wavered their vote; and given the nature of politics (then and sadly now) there were reports of bribery (never proven). It also helped Johnson that the potential replacement - at the time, new Vice Presidents were not installed as they would be under the 25th Amendment, it would have been the Senator Pro Tem (oldest member of the majority party) - was such a Radical Republican (Benjamin Wade was on record supporting Women's suffrage which horrified even the Radicals who supported the right of voting for Black (men)) that the moderates preferred Johnson over Wade. One other fear that had to have been in the backs of many a Republican Senator's mind was that a successful impeachment would have broken the independence of the Executive branch: from then on any President would have been terrified of getting impeached if he didn't do what Congress - even controlled by his own party - asked. While impeachment is a legitimate mechanism for removing from office someone who could abuse the office, there has to be a legitimate reason for doing so. And the Tenure of Office Act wasn't legitimate (future Supreme Court rulings confirmed the law was Unconstitutional).
Johnson's remaining tenure after the impeachment was brief and relatively uneventful, due to it being an election year. As for his impact on the nation, Johnson left a lasting legacy of racial politics that could have ended in 1865 instead of perpetuating until 1965.
Next week: A Really Bad President... But NOT for the Reasons His Critics Argued for a Century