When can POTUS authorize a nuclear attack? Peter Feaver answers on PBS NewsHour

"It's true that the President doesn't have to have his order 'Ok'd' by another person.  That there's not a two-man rule at the very top.  The President alone makes the decision.  But the President alone cannot carry out the decision.  There's ample opportunity for the rest of the system to put pressure, change the President's mind under a scenario of, say, preventive war." - Peter Feaver