Connecticut legislators are expected to pass sweeping gun-control legislation on Wednesday, becoming the third state since the Dec. 14 shooting in Newtown to do so.

But until recently, it wasn’t clear whether any legislation would even come to a vote. Connecticut has several strict gun laws in place — it was one of the few to pass a state assault weapons ban in 1993. But in recent years, the state’s pro-gun groups, using grassroots and legislative pressure, have killed two major pieces of gun-control legislation in a coordinated offensive. They strongly opposed any new laws after Newtown.

This time, though, something was different.

Local residents in support of gun-control began turning up at hearings that were once largely attended by gun advocates.

Connecticut Against Gun Violence, a local nonprofit group, said its membership has gained 35,000 supporters since Dec. 14, and now has about 45,000 on its rolls. Although it had traditionally operated in southern Connecticut, it began gaining supporters statewide. Recognizing an opportunity, CAGV ran radio advertisements and held a major march on Feb. 14, attended by an estimated 5,000 people, two months after the shooting.

New CAGV members, many of them suburban moms worried about putting their children on the school bus, couldn’t always make legislative hearings. So instead, they began calling legislators every Friday at 9:30 a.m., the time the shooting began at the elementary school on Dec. 14, reminding them of each week that passed without new gun-control legislation.

“The opposition was looking for the ‘Connecticut effect‘ to fade, and go away,” said Rob Pinciaro, the CAGV’s executive director. “It never did.”

Other groups sprung up, like the Newtown Action Alliance, which participated in an annual march in Hartford organized by Mothers United Against Violence, a Connecticut group that has long opposed handgun violence in urban areas. This year the march was dedicated to urging lawmakers to pass the pending bill.

“For the first time in 11 years, that was the first time I’ve seen suburbanites and urbanites united on the same thing,” said Rev. Henry Brown, a founder of Mothers United Against Violence. “Who wants to see babies taken like those babies were taken? We know that pain and grief because we lose ours every day.”

Brown said he would have liked the legislation to address handguns in addition to assault weapons, and hoped that would be legislators’ next priority. “But any kind of law that can regulate guns is something we need in our communities today,” he said.

Adding to the grassroots pressure were relatives of those killed in the shooting, some of whom appeared in ads sponsored by Mayors Against Illegal Guns that ran in Connecticut. Other national groups, including the Violence Policy Center and the Law Center to Prevent Gun Violence, offered suggestions on how to draft legislation in the state.

Pro-gun supporters also turned out in force at nearly every hearing. The National Shooting Sports Foundation, a Newtown-based group that represents gun manufacturers, began running radio ads arguing that new gun-control laws would drive companies out of the state, taking jobs with them.

The National Rifle Association also stepped in, paying for robocalls throughout the state urging people to oppose the legislation. But it may have pushed too far: Newtown residents still reeling from the tragedy were upset when they also received several of the calls. (The NRA defended the move to CNN, saying its members expect the group to keep them apprised of new legislation, but non-members also received the calls.)

Local pro-gun groups have argued that legislation would only infringe on gun-owners’ rights and do nothing to prevent tragedies like Newtown. Rich Burgess, the president of Connecticut Carry, another local pro-gun group, said in a statement Tuesday that lawmakers had ignored the views of pro-gun activists in proposing legislation that “aims to destroy the rights so many of us cherish in this state.”

“Instead of trying to address the nature of the horrific crime, the legislature has come up with proposals that clearly would not have prevented the massacre,” the statement said, adding, “The voting scorecard from this bill will not be forgotten or forgiven.”

The General Assembly has a Democratic majority in both houses and likely could have moved legislation without Republican backing. But in the weeks after the shooting, there were already indications that legislation might win bipartisan support this time.

State lawmakers with top ratings from the NRA began to reach out quietly to gun-control supporters to try to discuss how they might respond to the tragedy, according to one lobbyist familiar with the negotiations.

After a bipartisan taskforce formed in the General Assembly reached a deal on Monday, Lawrence Cafero, the House minority leader, told The New York Times there would be “substantial” Republican support for the bill. Lawmakers said they hoped to become a national model.

The legislation is some of the most comprehensive gun-control legislation being considered by a state nationwide. In the wake of Newtown, most states have been proposing pro-gun bills.

The Connecticut bill would expand its existing ban on assault weapons, and toughen penalties for firearms trafficking and illegal possession offenses. You can read the full set of proposals here, which also include plans to keep schools more secure and improve mental-health care. Here are some of the major gun provisions:

• A weapon offender registry: People convicted of one of 40 or more weapons offenses or other felony involving a deadly weapon would have to register with the government for five years upon their release from prison, checking in once per year with local law enforcement.
• Universal background checks: Effective immediately, every Connecticut resident seeking to buy any firearm must first pass a national criminal background check.
• Broader assault-weapons ban: Connecticut already has a ban on 66 firearms. This bill would add more than 100 new weapons to the banned list, along with some military-style features. Anyone who already possesses one of these weapons would have to register them.
• High-capacity magazine ban: Magazines that can hold more than 10 rounds can no longer be sold or transferred. Possession, purchase or importation into the state will be considered a felony.
• Eligibility certificates: Those who buy rifles or shotguns would be required to undergo a safety-training course, be fingerprinted and undergo a background check to receive a state-issued certificate authorizing possession.
• Ammunition sales restrictions: Only residents with an eligibility certificate or other legal authorization can purchase ammunition. Background-check is required.
• Access for the Mentally Ill: Anyone who has been admitted for psychiatric treatment — voluntarily or not — is prohibited for a period from receiving an eligibility permit for a firearm.

Sarah Childress, Former Series Senior Editor, FRONTLINE