Obama began examining how he could tighten the nation’s gun rules after October’s mass shooting at Umpqua Community College in Roseburg, Ore. Administration lawyers have spent months reviewing various proposals to make sure they can withstand legal challenges.

The idea of requiring informal gun dealers to obtain a license from the Bureau of Alcohol, Tobacco, Firearms and Explosives and of conducting background checks came up two years ago when White House officials drafted a proposal for dealers who sell at least 50 guns annually.

The idea was shelved because of legal concerns but gained new momentum after the Roseburg shooting. At that point, Democratic presidential candidate Hillary Clinton said she would pursue such a requirement by executive action if elected. Administration officials gave the proposal another look and determined it could be done in a way that was legally defensible.

The White House review has been conducted in relative secrecy, soliciting input from gun safety groups without specifying which policies the administration might ultimately adopt.