Division is brewing in Washington over just who is the biggest threat to American national security. The US President has warned the world to prepare for the threat of nuclear terrorism - but his Defence Secretary has a different take. Gayane Chichikyan has the story.br br RT LIVE br Subscribe to RT! br Like us on Facebook Follow us on Twitter Follow us on Instagram Follow us on Google+ Listen to us on Soundcloud: br RT (Russia Today) is a global news network broadcasting from Moscow and Washington studios. RT is the first news channel to break the 1 billion YouTube views benchmark.