One of the biggest mistakes, albeit in hindsight, Lincoln is thought to have made is making Andrew Johnson his running mate. There have been timelines on if Lincoln kept his original VP Hannibal Hamlin. Let's assume he does, and Lincoln is still shot. Andrew Johnson had a lot of symbolic promise for the unity Lincoln wanted to represent: he was a self-made man who'd remained loyal to the Union despite being a Southerner, showing quite a bit of courage. Though a slave holder, Johnson held a contempt towards the rich plantation class given his poor background. Had he never been chosen as Lincoln's running mate, never been president I believe we would've looked upon him a lot more fondly. But what would that legacy be of an Andrew Johnson who wasn't president in the shadow of Lincoln, instead a Democrat during the administration of Hamlin. And the potential successor to Hamlin, as without his opposition to Johnson it's not a guarantee Ulysses S Grant would decide to be the Republican nominee.