No wonder that, a century-and-a-half later, today's White House candidates continue to argue about what Lincoln would have done, how Lincoln might have led and whose agenda Lincoln might have endorsed. He remains both an inspiration and an aspiration.
But what if Booth had misfired on that April evening at Ford's Theatre? What if Lincoln had lived to lead? Would we still be exalting him as the greatest American president?
In a word, yes. True, post-Civil War Reconstruction proved too much for Lincoln's White House successor, the hapless and bigoted Andrew Johnson. And the same period would have tested even the politically savvy and sensitive Lincoln. But unlike Johnson, Lincoln had already sealed a preeminent reputation.
As he was signing the Emancipation Proclamation on January 1, 1863, Lincoln had confided to eyewitnesses at the scene: "If my name ever goes into history, it will be for this act."
And he was right. Black freedom, along with solidifying national authority and making the union permanent and powerful, would have stood as legacy achievements even if peacetime unity had unraveled during a second Lincoln administration.
That said, Lincoln would have been required to summon all his skills of persuasion to forge what he called, in the inaugural address he delivered just six weeks before his death, "a just and a lasting peace among ourselves and with all nations."
Had Lincoln lived, the punitive Republican supermajority in Congress would have been just as reluctant to readmit Democratic Southerners to their pre-war seats, just as determined to disenfranchise Southern whites as they enfranchised Southern blacks.
It's of course impossible to predict whether Lincoln's survival might have meant a cleaner path to reunion and reconciliation, and toward the truly equal biracial society that has eluded us ever since.
One thing is certain: In what proved to be his final speech three evenings before his death, Lincoln had become the first president ever to support black voting. John Wilkes Booth, who lurked on the White House lawn that night as Lincoln spoke from a second-floor window, muttered, "That means n----r equality. That's the last speech he'll ever make." And he soon made good on his threat. We should take Lincoln at his word.
He would have fought for and perhaps secured black voting rights in the postwar North and South.
He would surely have taken up cherished and deferred domestic priorities, too, particularly "internal improvements" as they were called: roads, canals, bridges, and railroads -- projects he had long championed. Lincoln might well have become "the infrastructure president."
Free college for all? Lincoln had signed the law authorizing the first land grant colleges, schools that evolved into today's state universities, not to mention Cornell. Count on his becoming the "education president," too.
Above all, had Lincoln lived to continue the second American Revolution that ended slavery by the 1860s, the third revolution --the civil rights movement of the 1960s -- might not have been necessary. He was that gifted.
We will never know any of this for sure, but one thing is certain: Hillary Clinton, Donald Trump and even Libertarian Gary Johnson (via a bizarre five-minute TV spot featuring a top-hatted Lincoln re-enactor
) have all tried evoking Lincoln this year. One of them will be elected in November to continue what Lincoln once called the nation's "unfinished work" of uniting us. Without Lincoln, the right to choose our next national leader might have been lost altogether. With him, however -- had he lived -- we might not be facing half the nagging crises that still plague us.