"There are many single-issue gun rights voters and Republicans who now control the House of Representatives and know it's a bad move to vote (against the NRA)," said Melzer said. "That's a sure way to ensure there will be a primary opponent."

In the meantime, gun control advocates are hoping to capitalize on the bizarre rhythm that has become all too familiar in the wake of the nation's mass shootings.

However, when the NRA goes quiet, the normally outgunned opposition moves into high gear.

That's because they know that after they mourn for the dead, there's not much time, money or a broader platform to make their case for change before most people move on in their lives, said Mark Glaze, director of Mayors Against Illegal Guns. His group has spent 20-hour days on staff calls, legislative strategy sessions and fielding calls from gun violence survivors and celebrities and mayors who want to sign on.

"Look," Glaze said, "when this kind of thing happens, we have to make the case in that very short window -- what went wrong, why it went wrong, how you can fix it -- in a way that motivates Congress to do what it should."

The Brady Campaign to prevent Gun Violence was on Capitol Hill on Tuesday with members of a new community group, Newtown United.

Josh Horwitz with the Coalition to Stop Gun Violence said his group just hired temporary staff to deal with hundreds of new volunteers who want to help after Newtown.

"It depends on the shooting," Glaze said. "With something as terrible as this is, involving children, the window is open a little wider than it has been before. I think my back of the envelope is usually about a month. But after the series of mass shootings and the gravity of this one, I think we may have a little more time."