"Chipman said he supports Congress acting to ban all "assault weapons" and AR-15s."
"The AR-15 is a gun I was issued on the ATF’s SWAT team, and it’s a particularly lethal weapon. Regulating it as other particularly lethal weapons, I have advocated for. As ATF director, if I’m confirmed, I would simply enforce the laws on the books, and right now there is no such ban on those guns."
As I recall the crux of that argument was that it's unlikely to make it through the senate. Sounds like this guy acknowledges such regulation would require congressional action and isn't going to make a unitary executive argument.