Sentence:  Capitalizing on the restive mood, Mr. Farage, the U.K. Independence Party leader, took out an advertisement in The Daily Telegraph this week inviting unhappy Tories to <WSD>defect</WSD>. In it Mr. Farage sniped that the Cameron government — made up disproportionately of career politicians who graduated from Eton and Oxbridge — was “run by a bunch of college kids, none of whom have ever had a proper job in their lives.” 
Meaning of the word marked with <WSD> tags:  To abandon or turn against; to cease or change one's loyalty, especially from a military organisation or political party.