If a background check shows that you are an undocumented immigrant, federal law bars you from buying a gun. If the same check shows that you have ties to Al Qaeda, you are free to buy an AK-47. That is the absurd state of the nation's gun laws, and a recent government report revealed that terrorist suspects are taking advantage of it. There are a few promising signs, however, that the federal government is considering injecting some sanity into policies on terror suspects and guns. The Government Accountability Office examined F.B.I. and state background checks for gun sales during a...