I asked that -- about John McCain -- on other threads a week or so ago. It's pretty surprising that Arizona constituents aren't taking him to the woodshed.
His not voting today is smoke-and-mirrors (IMHO) because last year he criss-crossed the state trying to defeat prop 200 (which passed handily). He doesn't want to be saddled with a vote next year when he starts campaigning for President, but I think it's too late and not voting speaks volumns. I read that the Minutemen visited his office last Friday and his staff insisted they leave or they were going to call the Capital Police. Even Hagel didn't give them that kind of reception.