mav·er·ick

1. Southwestern U.S. an unbranded calf, cow, or steer, esp. an unbranded calf that is separated from its mother.
2. a lone dissenter, as an intellectual, an artist, or a politician, who takes an independent stand apart from his or her associates.
3. (initial capital letter) an electro-optically guided U.S. air-to-ground tactical missile for destroying tanks and other hardened targets at ranges up to 15 mi. (24 km). [Origin: 1865–70, Americanism; after Samuel A. Maverick (1803–70), Texas pioneer who left his calves unbranded]

—Synonyms 2. nonconformist, independent, loner.

(h/t VentureBeat)

John McCain, an unbranded steer indeed.