WASHINGTON - Russia presents the greatest threat to US national security and its behavior is "nothing short of alarming," Marine General Joseph Dunford, the nominee to become chairman of the Joint Chiefs of Staff, said at his Senate confirmation hearing on Thursday."My assessment today, Senator, is that Russia presents the greatest threat to our national security," said Dunford, the commandant of the Marine Corps, noting that Russia was a nuclear power capable of violating allies' sovereignty."So if you want to talk about a nation that could pose an existential threat to the United States, I'd have to point to Russia. And if you look at their behavior, it's nothing short of alarming."Relations between Moscow and the West have plunged to a post-Cold War low since Russia annexed Ukraine's Crimea region last year.