Pakistan. You name the problem, Pakistan seems to have it: jihadist terrorism, ethnic strife, disputed borders, endemic corruption, and a weak government that seems weaker at every pass. Oh, and it has nuclear weapons, scientists who go on the road to sell them, and a series of governments that openly back the Taliban, among other nasty movements. Under President George W. Bush, and then under Obama, the United States tried to work with Pakistan while at the same time never trusting it -- a policy mirrored by the regime in Islamabad, which believes with good reason that the United States is a fickle ally. This unhappy approach may be the best that can be managed given the lack of strong pro-U.S. voices in Pakistan, but the prospect for even more serious unrest in Pakistan is of grave concern. Even worse, Pakistan has tolerated, or supported depending on your view, terrorist attacks on India, raising the possibility of a war between two nuclear-armed states. Such a war might leave thousands dead or, if it goes nuclear, millions. The environmental costs would be global, stunting agriculture, and posing health problems that would last for generations.