Let's start with the dictionary Definition with these two meanings being relevant:
–noun
- Southwestern U.S. an unbranded calf, cow, or steer, esp. an unbranded calf that is separated from its mother.
- a lone dissenter, as an intellectual, an artist, or a politician, who takes an independent stand apart from his or her associates.
A quick google check shows that McCain has used that word at least 1293 times since the beginning of his campaign. I guess you could say this is an attempt at creating a brand, a single word that is a universal identifier. Given the word's original meaning, "cattle without a brand stamped on their body, this alone would be ironic. But there is more:
Today's New York Times article, "Who You Callin' a Maverick" describes the eponymous Samuel Augustus Maverick, whose descendants are rather angry at John McCain arrogation of this noble family name.
"I’m just enraged that McCain calls himself a maverick," said Terrellita Maverick, 82, a San Antonio native who proudly carries the name of a family that has been known for its progressive politics since the 1600s, when an early ancestor in Boston got into trouble with the law over his agitation for the rights of indentured servants.
In the 1800s, Samuel Augustus Maverick went to Texas and became known for not branding his cattle. He was more interested in keeping track of the land he owned than the livestock on it, Ms. Maverick said; unbranded cattle, then, were called "Maverick’s." The name came to mean anyone who didn’t bear another’s brand.
Sam's grandson Fontaine Maury Maverick was the first to engage in politics, losing his position as Mayor of San Antonio when conservatives pulled what is a McCain staple, accusing him of being unpatriotic. He then served honorably in in FDR's administration during the war.
Fontaine's son, Maury, was the embodiment of the progressive passion we on this site dream of the current democratic party becoming:
This Maverick’s son, Maury Jr., was a firebrand civil libertarian and lawyer who defended draft resisters, atheists and others scorned by society. He served in the Texas Legislature during the McCarthy era and wrote fiery columns for The San Antonio Express-News. His final column, published on Feb. 2, 2003, just after he died at 82, was an attack on the coming war in Iraq.
The final word on this subject is this quote by Maury sister, Terrelita Maverick, a proud member of the ACLU:
(John McCaini)s in no way a maverick, in uppercase or lowercase."
"It’s just incredible — the nerve! — to suggest that he’s not part of that Republican herd. Every time we hear it, all my children and I and all my family shrink a little and say, ‘Oh, my God, he said it again.’ "
"He’s a Republican," she said. "He’s branded."