There's a lot that can be done without congress using executive authority only.
Bloomberg has already laid out a blueprint:
http://www.pagunblog.com/2009/12/28/blo ... blueprint/
That's all pretty easy stuff to do.
On Bloomberg's list, the low hanging fruit is banning imports of guns and ammo. It is illegal to import any gun that is not appropriate for "sporting purposes." AG Eric Holder makes the rules as to what that means. So imports of anything from Glocks to AK-47s to nice high-priced semiauto shotguns could be banned with a stroke of the pen tomorrow. Banning ammo would make prices go up even more; a lot of our ammo comes from abroad now, and it isn't just the Russian calibers. For example, PMC comes from Korea, Prvi Partizan comes from Eastern Europe, Wolf comes from Russia, etc. Even if you don't personally buy PMC, all the folks who did buy PMC will now have to buy Federal, Winchester, etc which will raise prices for everyone. Supply/demand.
The Justice Department can obviously also hassle FFLs tremendously. I actually just let my C&R lapse so that I don't have to worry about their bullshit.
Every single 20 and 12 gauge shotgun is a destructive device regulated under the NFA unless it is appropriate for sporting purposes because they have bores over 50 caliber. Again, AG Eric Holder decides what "sporting purposes" means. The administration could state that a shotgun with pistol grip, adjustable stock, buttstock shell carrier, semiautomatic action, capacity greater than three shells, etc is inappropriate for sporting purposes and thus is a DD. Possession of an unregistered DD is a felony.
It is already a felony to get within 1000 yards of a school with a firearm unless (A) you have a CWP from that state (ATF does not recognize reciprocity) or (B) have the weapon unloaded in a locked case in your vehicle. There is no exemption for driving on a highway by a school. It could be possible to use TSA VIPR teams augmented with an ATF or FBI rep to bust people for violating the Gun Free School Zones act.
The ATF could make illegal demands on FFLs or others. For example, they've demanded long gun registration of certain rifles from FFLs in the southwest since 2011. They have no statutory authority to do so, and in fact, their action probably violates federal law, but NRA hasn't found a judge who will suspend the demand yet. So it is still in effect. There's a lot that could be done to hurt the industry and gun owners using questionable demands from ATF or EOs that are later tossed by a court (or maybe not) years down the road.
There are many, many things that the administration can do without congressional action to screw gun owners. Elections have consequences and Americans voted for this. Pres Obama's position on firearms has been clear and consistent for decades.