Defense Secretary Chuck Hagel has concluded that problems in the nation’s nuclear forces are rooted in a lack of investment, inattention by high-level leaders and sagging morale, and is ordering top-to-bottom changes, vowing to invest billions of dollars to fix the management of the world’s most deadly weapons, two senior defense officials told The Associated Press on Thursday. Hagel ordered two lengthy reviews of the nuclear force after a series of stories by the AP revealed numerous problems in management, morale, security and safety, leading to several firings, demotions and other disciplinary actions against a range of Air Force personnel...