A bunker mentality is a slang phrase for a phenomenon that occurs when a group or individual stops taking new, pertinent information into account, and begins viewing outsiders as enemies, due to an isolation resulting from being under attack. Political campaigns and figures are often accused of having this mentality, particularly when a leader, administration or party has become unpopular or is in some sort of trouble.

The phrase is taken from an analogy to soldiers that have taken shelter in a bunker while under siege from enemies.

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