I believe the questions should be asked: how dangerous is John McCain?
Ezra Klein answers the question. Very dangerous.
Between 1995 and 2008, McCain has advocated full-scale war in Kosovo, North Korea, Iraq, and Iran. He has repeatedly sought to ratchet up tensions with Russia and China, and has advisers who've called for air strikes on Syria.
Does this necessarily tell us how McCain will behave in office? No, but I think it should be a warning.