In an editorial calling for withdrawal from Afghanistan, National Review's John J. Miller raises a tricky question:

[W]hy will the fall of part or all of Afghanistan to the Taliban and its al-Qaeda allies endanger Pakistan? For over a decade the Taliban harbored al-Qaeda and controlled Afghanistan. The Pakistani government not only did not fail; it was far more stable than it is today. There are no signs that Pakistan’s strong army, infrastructure, and nuclear weapons will fall to its own Taliban. But if it does so, it will be because of Pakistan’s corruption, illiteracy, tolerance of modern slavery, incompetence, lack of government or popular will, and disdain for the West — not because of who rules its sparsely populated, weaker neighbor.

That could be right. The flip side is that Pakistan's government is weaker now than it was when the Taliban ruled Afghanistan. And the indigenous Islamist radicals within Pakistan seem to be far stronger, and would likely be strengthened and emboldened by a neighboring Afghanistan again mostly or entirely controlled by the Taliban. Or so the White House thinking goes, it seems.