Certain writers use a chess metaphor to explain Lincoln's mindset about defending Washington: Lincoln would not exchange queens with the Rebels. That is, he would not trade Washington for Richmond.
If the Civil War public ever heard and understood that metaphor, it was thanks to the newspaper coverage of the American prodigy Paul Morphy, a youth who challenged the chess world to achieve remarkable success.
My first exposure to the Civil War era, apart from John Wayne's Horse Soldiers, was through the study of the games of the great Paul Morphy of New Orleans, the uncrowned world champion who died the death of a Russian novel. The Civil War, I learned as a child, had killed his interest in the game as well as cut off his career at the height of his fame and power. The war eventually made him mad. Chess-playing American kids of my youth knew Paul Morphy's story, if not his games.
I remembered Morphy and Lincoln last night looking through Jeremy Silman's 1999 chess study, The Amateur's Mind. Silman was analyzing a game against one of his students. He has a harsh commentary style I like very much:
Also note his fear concerning the position of the White King. [...] Amateurs tend to panic in the face of any kind of kingside threat, and his comments show that he suffers from the same "King-safety" disease.
Lincoln, unfortunately, was not taking strategy lessons from chess experts and seems to have suffered more than a little "King-safety disease" in March/April 1862. Silman continues:
King safety is very important! But only worry if the enemy has some pieces aimed in your King's direction.
Think about the Eastern theatre in March and April, 1862.
In the present position, the only pieces Black has on the kingside are his f6-Knight and the e7-Queen; this can hardly be construed as a horde of attackers!
I'm picturing an pack of unsupported ragamuffins having a run up the Valley.
And, more disturbingly, I'm picturing Jefferson Davis consulting a Louisiana chess prodigy on strategy. There's some scary alternative history for you.