Protecting the nation's security has proved a daunting task for Pakistani Prime Minister Nawaz Sharif since he took office in mid-2013. But the number of challenges on his plate seems to have grown over the past few months. Tensions are once again rising between Pakistan and its nuclear neighbor, India. At the same time, Sharif's administration is struggling to contain the fallout from a widely read Oct. 7 expose accusing the military of undermining Islamabad's efforts to combat the country's militancies. As if this were not enough, the government is also working furiously to piece together the events leading up to a deadly Oct. 24 attack on a police academy in Quetta that killed at least 60 people. On the surface, this may appear to be a chain of disparate events. Yet they are, in fact, linked by a common thread: the military's outsize influence in Pakistani policymaking....