Which he has no legal authority to do.
Via LA Times:
White House officials are seeking a way to use executive authority to close the so-called gun show loophole that allows thousands of people to buy guns each year without a background check, but complicated legal issues have slowed the process.
Almost three years ago, President Obama asked Congress to change the law to require background checks for weapons sold at gun shows, but a bill to do so died in the Senate – dashing administration hopes for legislative action to address the loophole.
Efforts to use Obama’s executive powers to address the issue took on added urgency in October, when a shooter at a community college in Oregon killed nine people, then shot himself.

