In the wake of the San Bernardino killings, the suggestion has been made to deny gun purchases to those on the no-fly list. While this makes some sense from a security viewpoint, there's a serious legal issue with the idea.
The no-fly list is administrative. No one has a constitutional right to board an airplane. Consequently, the federal government can deny boarding to anyone it pleases. The grounds on which it does so are secret, and are generally based on intelligence.
By contrast, the Supreme Court has ruled that the Second Amendment guarantees the right to own a gun, at least a hand-gun. It is hard to imagine that the Supreme Court (or any other court) would permit a constitutional right to be violated without due process. But such due process is incompatible with the secret nature of the intelligence used to construct the no-fly list.
Before we rush ahead in our eagerness to "do something" about the terrorist threat, let's think about the implications of our proposals.