They will shoot for the moon......... gun show loophole, new AWB. But the one thing I think they have the best shot at will be a hi-cap mag ban.
1.) EO banning importation of firearms (just like what happened with Chinese firearms and ammo.
2.) EO banning imported ammo.
3.) Mandatory registration of "assault weapons" with failure to comply being a federal crime. No grandfather clause. You could be busted for mere possession.
4.) Big taxes on ammo (can also be pursued at the state level.)
5.) Having the BATFE "re-interpret" existing laws to criminalize classes of firearms.
6.) Having the EPA go after lead ammo.
7.) Ramming the UN Small Arms Treaty through a Senate willing to act due to a high-profile shooting and not wanting to look like "bad guys" for opposing it.
8.) A ban on "high-capacity" magazines as a "reasonable measure" that could probably sail through congress in the wake of this shooting.
9.) Going after their favorite invented bogeyman of the so-called "gun-show loophole".
10.) Assault Weapons ban, if they think they can get it through. They may go for it anyway because they can demonize "evil Republicans" and it is a win-win for them.
11.) Federal (DOJ), state, and municipal lawsuits against gun manufacturers.
12.) Using safety to prohibit multiple weapons like California has done with their infamous "drop test" with has banned things like the good-old S&W Model 10 revolver. Yep, the older Model 10s just don't measure up as safe. What's even worse, is that the guns on the approved list have to have their approvals renewed. Gun approvals expiring have been eliminating guns from the list. "Oops, looks like you can't buy that gun anymore. it's no longer on our little list." Anybody from CA please correct me if I'm in error on this one.
And that's just what I could think up at a moment's notice. They can do a lot without having to attempt an outright ban or confiscation.