What is the source of the allusion in the sentence below?
The mayoral candidate was widely viewed as quixotic, so it was no surprise that he lost by a substantial margin.

 - Greek mythology
 - literature
The source of the allusion quixotic is literature.
Don Quixote is the main character in Miguel de Cervantes Saavedra's novel of the same name. Quixote cannot see the world as it truly is; in his overly romanticized view, inns are castles and windmills are giants.
The allusion quixotic means naively idealistic.