A friend once told Abraham Lincoln he was concerned about Cabinet Officer Salmon Chase's ambition for the presidency, and he thought Lincoln should ask Chase to resign. Lincoln had observed that Chase's department was functioning very well, and as long as it continued to do so he would not worry about Chase's presidential aspirations.
To drive the point home he told of a time when he and his step-brother were plowing a cornfield in Indiana, he was driving the horse and his step-brother guiding the plow. The horse, naturally lazy and slow, suddenly rushed across the field so fast the boys could hardly keep pace with him. On reaching the end of the furrow, Lincoln discovered an enormous horse-fly fastened to the horse and knocked it off. His step-brother asked why he did that; whereupon Lincoln explained that he didn't want the horse bitten.
"But," protested his step-brother, "that's all that made him go!" "Now," said Lincoln, "if Mr. Chase has a presidential horse-fly biting him, I'm not going to knock it off if it will only make his department go."