My thinking is this: the Sandy Hook shooting really did affect people, including politicians. Some politicians are complete sociopaths (on both the left and the right), but most have at least some conscience. I suspect the gun-control advocates go through periods (like everyone) when they don't feel as energized about their position. If we go through long periods without a lot of massive, well-reported gun violence, it's not only their basis that erodes, it's their will to fight their cause. After all, if no one went into a mall, a school, a Wendy's, etc. and shot a bunch of innocent people up, there'd be no reason to control guns.
Undoubtedly, a few gun-control-advocates (I don't want to call them liberals, because I would generally be called liberal, but I'm against all but the most basic and reasonable kinds of gun control--no guns for people currently incarcerated, no private ownership of nuclear weapons, that sort of thing--people who are for gun-control do not understand history very well, IMO) are attempting to enforce a kind of fascist deprivation of the ability of individuals and the citizenry as a whole to maintain and defend general liberty. But most probably sincerely believe that gun control will prevent the sort of abomination we saw last week.
They're wrong, of course. But I don't suspect most gun-control advocates have a disingenuous motive.
I'd be happy with an assault weapons ban if there were some kind of assurance that, in the event people generally wanted to revolt, they could get their hands easily and readily on assault weapons and armor-piercing rounds. I can imagine a few potentially good suggestions about how that might work. But none of them are ever likely to be implemented.
In the meantime, what we really need to focus on is proper treatment for people who are mentally ill, and even more importantly, prevention of mental illness. The violence we experience as a society is due to the way we are, not the fact that guns are readily available. Gun control would be like putting a paranoid schizophrenic in a gag and a straightjacket, and proclaiming him cured because he can't do anything that seems crazy any longer...