I've been trying to make this point to friends who are firearm prohibitionists. The "terrorist watch list" is a thing that should not even exist; if you have evidence then arrest and charge the person, otherwise leave them alone. That's due process 101. It's sad that so many on both the so-called "left" and "right" are so willing to throw that basic value under the bus.
Indeed, the whole concept of background checks is based on a list of bad guys. But if you have a list of people you can' t trust with access to firearms, you have a list of people who need to be under supervision -- prison, parole, probation, or mandatory psychiatric care. It's the responsibility of those supervisors to keep those people away from guns, not the responsibility of someone selling Grandpa's old hunting rifle at an estate sale.
Whatever you think of gun control, Obama's assertion that "Closing the No-Fly List loophole is a no-brainer" is pretty brainless.
The no-fly list, a notorious, secretive, evidence-free zone in which Americans and foreigners alike are denied the freedom of movement based on secret, sloppy evidence that no is allowed to see or refute, is a terrible proxy for "people who should be treated as suspicious."