How does the concept of commander damage work in Magic: The Gathering, and what are the implications of accumulating commander damage during a game?

In Magic: The Gathering, commander damage is the amount of combat damage dealt by a player's commander to another player directly. If a player's commander deals a total of 21 or more commander damage to a player over the course of a game, that player loses the game. Accumulating commander damage can be a strategic way to eliminate opponents or force them to change their gameplay to avoid being defeated by commander damage.