One of the most common American proverbs, “Never swap horses in midstream,” is indelibly associated with Abraham Lincoln. The observation is a distillation of more extended remarks that Lincoln made on June 9, 1864, to a delegation from the National Union League who had come to the White House to congratulate him on his nomination for a second term as President. What Lincoln said was: “I do not allow myself to suppose that either the convention or the League have concluded to decide that I am either the greatest or best man in America, but rather they have concluded that it is not best to swap horses while crossing the river, and have further concluded that I am not so poor a horse that they might not make a botch of it in trying to swap.”

This bit of folk wisdom seems to have arisen as the punch line of a joke that was told in the 1840s about an Irishman (in other versions a Dutchman, probably meaning a German). Whatever his background, the poor fellow was crossing a stream on a mare, with a colt in tow. Falling off the mare, he grabbed the colt’s tail as it swam toward the bank. Onlookers yelled that he should take the mare’s tail instead as she was the stronger swimmer. But the man held fast to the colt, shouting in reply that this was not a good time for him to change horses.

Lincoln’s elevation of the old joke into a metaphor quickly caught on. Harper’s Weekly ran a political cartoon based on the idea in its issue dated November 12, which came out as Lincoln was about to defeat George B. McClellan at the polls.

The image has endured: Democrats used “Don’t swap horses in the middle of the stream” during Franklin D. Roosevelt’s re-election campaigns of 1940 and 1944. Earlier, in 1932, when FDR first ran for President and the nation’s economy was in shambles, wags suggested that the Republican motto must be “Don’t swap barrels while going over Niagara.” The metaphor has even crossed the Atlantic. Arnold Toynbee wrote in Civilization on Trial , “‘Herodianism’ … is a form of swapping horses while crossing a stream, and the rider who fails to find his seat in the new saddle is swept … to a death.”

It is thanks to Lincoln’s imprimatur that the phrase has become a permanent part of our lexicon.

—Hugh Rawson