We can keep fighting the Taliban—and probably keep them from retaking strategic positions—but it will remain at best a stalemate; we simply cannot amass enough troops to defeat them or stabilize the country.
A solution has to involve Pakistan. The Pakistani leaders, whoever they are, will not tackle the Taliban on the border unless they think that the mission is feasible and in their security interests. This is Political Science 101. So, we (or NATO or some group or groups of nations) have to help train and supply the Pakistani military to go after Taliban insurgents. We have to help relax tensions between Pakistan and India so that building up troops to the Afghan border won't seem to be a diversion. (Helping settle the two countries' dispute over Kashmir might be a start.) And we—in this case, the new American leaders—have to move away from Musharraf, whose future seems dim, and back the parliamentary leaders.
Finally, the security of Pakistan and Afghanistan—a subject that involves not just global terrorism, but nuclear weapons—is a regional issue. It was always a bit of a delusion, a post-Cold War dream, to think that NATO could handle this. The nations of the region have to be brought in—including Iran. The very phrase induces nightmares, but a "grand bargain" of some sort has to be struck. The nations involved in this bargain have so many disputes, so many conflicting interests, it is hard to imagine what the outlines of such a deal would look like. But it's very easy to imagine what kind of nightmare the alternative might look like. So there's no choice here; we have to try.
In other words, there is no military solution (and rarely is there, when dealing with insurgencies.) The solution must be political and diplomatic. The first step in a political solution is of course to change the political climate here, removing a President who has at best been disinterested in Afghanistan and replacing him with one who acknowledges that the future of Afghanistan is as critical to us-if not moreso-than the future of Iraq. Kaplan doesn't outline what a "grand bargain" would entail, because there is no way to know at this point. Only after talks with Iran, Pakitan, India and so on could we even begin hammer out details of what sort of regional cooperation it would require to settle Afghanistan. In the past it's been easy to ignore Afghanistan, as the Afghans largely warred with themselves. Long before 9/11 however, Afghanistan became the home of violent Islamic terrorists who regard it as a holy mission to kill Americans, and isn't likely to change anytime soon. The potential cost of ignoring Afghanistan is simply too high for us to accept the status quo any longer.