Senator John McCain, who faced down his captors in a Vietnam prisoner of war camp with jut-jawed defiance and later turned his rebellious streak into a 35-year political career that took him to Congress and the Republican presidential nomination, died Saturday after battling brain cancer for more than a year. He was 81. McCain was elected to the Senate from Arizona six times but twice thwarted in seeking the presidency. McCain returned to the Senate in 2009, determined not to let that defeat define him.