In response to Chris Murphy's 15 hour filibuster, Democrats will get a vote on several gun amendments to an appropriations bill, one mandating background checks for all gun purchases, another doing some kind of check to ensure the purchaser is not a known or suspected terrorist.
The latter amendment is Dianne Feinstein's (see Greg Sargent's piece on it here). It started as a straight check against the No Fly list (which would not have stopped Omar Mateen from obtaining a gun), but now has evolved. It now says the Attorney General,
may deny the transfer of a firearm if [she] determines, based on the totality of the circumstances, that the transferee represents a threat to public safety based on a reasonable suspicion that the transferee is engaged, or has been engaged, in conduct constituting, in preparation for, in aid of, or related to terrorism, or providing material support or resources therefor.
[snip]
The Attorney General shall establish, within the amounts appropriated, procedures to ensure that, if an individual who is, or within the previous 5 years has been, under investigation for conduct related to a Federal crime of terrorism, as defined in section 2332b(g)(5) of title 18, United States Code, attempts to purchase a firearm, the Attorney General or a designee of the Attorney General shall be promptly notified of the attempted purchase.
The way it would work is a background check would trigger a review of FBI files; if those files showed any "investigation" into terrorism, the muckety mucks would be notified, and they could discretionarily refuse to approve the gun purchase, which they would almost always do for fear of being responsible if something happened.
Read the full story at EmptyWheel.net