Rick Hertzberg:

Along with its various derivatives, 'misspeak' has become one of the signature verbal workhorses of this interminable political season, right up there with 'narrative,' 'Day One,' and 'hope.' It carries the suggestion that, while the politician's perfectly functioning brain has dispatched the correct signals, the mouth has somehow received and transmitted them in altered form. 'Misspeak' is a powerful word, a magical word. It is a word that is apparently thought capable, in its contemporary political usage, of isolating a palpable, possibly toxic untruth, sealing it up in an airtight bag, and disposing of it harmlessly.

(Hat tip: Goddard).