Alex Koppelman has an in-depth analysis:

Anything is possible, especially in the wake of something like the Newtown shooting, but it’s difficult to see the political calculus that leads to a few dozen Republicans switching sides on this. Just as the makeup of the House Democratic caucus has changed, becoming more liberal, the G.O.P. side has become filled with members who don’t have to fear a Democratic opponent but need to be concerned about a primary challenge from their right. Still, many Democrats remain optimistic that something can get done, that Newtown has altered the congressional math on this issue. 

He also notes an outside-spending wrinkle:

In a post-Citizens United world, the N.R.A.’s coffers, which had once seemed so threatening, could easily be matched by a few rich supporters of gun control—or even just one.

Margaret Talbot hopes people will take to the streets to keep the pressure on Congress:

On Monday, demonstrators for gun control gathered outside the N.R.A.’s lobbying headquarters in Washington. They read aloud the names of the children who died in 158472106Newtown, and they read aloud the talking points that the N.R.A. uses in its lobbying. There were only about two hundred people there, and I saw some gloating about that turnout in the blogs and Twitter feeds of gun-rights advocates.

Maybe they’ll be proven right, and the movement will sputter out again. But if it doesn’t, the value of it is clear. By the time Congress is back in session and ready to take up gun control, Newtown will be fading a little in the public memory. It’s hard to imagine it now, but that’s what’s happened after every mass shooting of the last several years. The gun-rights advocates will be as single-mindedly impassioned as they always are, and the rest of us will be thinking of other things.

But rallies and marches and demonstrations could remind those who’ve forgotten of what happened, serve to back up the members of Congress who want to do something about guns, and signal that there are numbers and votes on the other side as well. It’s simple—but it matters.

(Photo: Protesters on December 17 with the social activist group CREDO descend on the offices of the NRA's Capitol Hill lobbiest's office demanding the pro-gun lobby stand down in reaction to the shooting at Sandy Hook Elementary School. A leading Democratic senator launched a bid Sunday to ban assault weapons in the wake of the latest deadly US school shooting, announcing that she will put a bill before Congress on January 3. Dianne Feinstein, the influential chair of the Senate Intelligence Committee, said she believed President Barack Obama would support her legislation, also aimed at outlawing magazines carrying more than 10 bullets. By Paul J. Richards/AFP/Getty Images)