Slipping off to Syria over the weekend and urging a greater U.S. military role in the ongoing crisis, Republican Sen. John McCain remains a thorn in President Obama’s side even as he tackles his own party by siding with the administration on key issues from gun safety to immigration reform. That’s the definition of a maverick, a label McCain embraced when he ran for president in 2000 and 2008 but then disavowed in 2010 when confronted with a primary challenge from the right in his bid for reelection in Arizona.