"Remembering" Lincoln's death? Come on, OM, one senior to another: you can't really be THAT old!
I've often wondered the same thing about Lincoln (and, with regard to Vietnam, about Kennedy, who was completely disillusioned about the war in November, 1963.) In the end, I suspect he couldn't have stopped Jim Crow - those laws were in the hearts and minds of the vanquished, who weren't particular fans of Lincoln (his election was why they seceded in the first place.) Likewise, given his somewhat divisive cabinet (think Team of Rivals), and a Congress that did not see eye to eye with him, and was bent on making the South pay, a gentler Reconstruction may not have been a political possibility. (It certainly wasn't when U.S. Grant, who also favored a gentler reconstruction, took office after Johnson a few years later.) Lincoln might have softened the burden on the freed slaves, perhaps done more to educate them, and might have eliminated much of the sectional hatred between Northern carpetbaggers and Southern landowners. But, in the end, his second term might have fizzled out on him. (And, again, the same might have happened to Kennedy.)
In another "good episode of Star Trek" vein, the Lincolns were looking for another couple to take with them, to share their box. The first choice was Ulysses and Julia Grant; they declined due to "pressing Army business" (though "Julia really doesn't like Mary" may have been more accurate.) Had they both been in the box, we might have lost a sitting president and a future president. (I can't remember though: did Booth's gun have more than one bullet?)