The relationship between Abraham Lincoln and General George McClellan began with great promise and went steadily and quickly downhill. Given that the two men were such complete opposites, maybe the failure of their partnership was inevitable. Privately, the spectacularly popular McClellan joined in the general ridicule of Lincoln, calling him "The Gorilla" and "nothing more than a well-meaning baboon." Lincoln, who was frequently likened to some sort of ape by his detractors because of his gangly arms and dark brows, spent long hours studying military books drawn from the Library of Congress, hoping to put himself on a better footing with his professional generals. But his diligent attempts to learn the soldier's trade only made him more ridiculous to the elegant, vain McClellan, whose digs at Lincoln were freely passed around Washington.

In an army made up largely of volunteers, there was nothing ridiculous or unusual about Lincoln's crash course in the art of war—this was precisely how Joshua Lawrence Chamberlain, the Medal of Honor-winning hero of Gettysburg, rose from amateur soldier to brigadier general. But early in the war the entrenched professional officers, represented most publicly by McClellan, were a long way from being ready to acknowledge the abilities of volunteer strategists, in the camps or in the White House.

Lincoln was well aware of McClellan's habit of scoring points at his expense. To the many who expressed astonishment at his tolerant attitude toward McClellan's insults, he replied:

What’s the harm in letting him have his fling? If he did not pitch into me, he would into some poor fellow he might hurt.

The cautious, gifted, methodical McClellan was driven to commit his most arrogant offense by Lincoln's constant pressure for an advance by the long-dormant Army of the Potomac. In a presidential snub rivaled only by Douglas Macarthur leaving Harry Truman fuming on an airstrip a century later, McClellan left the President waiting for him in his sitting room while he went to bed. Typical of Lincoln's pragmatism was the remark, "I'll hold McClellan's horse if he'll only bring us success."

John Hay, Lincoln's young assistant secretary, was fascinated by Lincoln's ability to subordinate his feelings to a larger purpose. Lincoln once explained his tolerance to a hot-tempered associate advocating revenge for some sin committed against the president.

You have more of that feeling of personal resentment than I. Perhaps I may have too little of it, but I never thought it paid. A man has not time to spend half his life in quarrels. If any man ceases to attack me, I never remember the past against him.

Even so, John Hay wrote that Lincoln got into the habit of summoning McClellan to the White House from then on, never visiting his home again.