Harold Holzer is the Jonathan F. Fanton Director of The Roosevelt House Public Policy Institute at Hunter College in New York City and has written 52 books on Abraham Lincoln and the Civil War.

(CNN) On Good Friday 1865, actor-turned assassin John Wilkes Booth not only ended a great American life in progress, but made his victim -- Abraham Lincoln -- seem exponentially greater in death. Ever since the 16th president died, nine hours after Booth fired his fatal shot, American presidents have been judged against the myth that replaced the man. The savior of the union, great emancipator and martyr of liberty has proven an all but impossible act to follow.

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.

Lithograph commemorating president Abraham-Lincoln's 1862 Emancipation Proclamation freeing slaves in the Confederate states, 1865.

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."

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