The Connecticut shootings occurred three days after the incident in Oregon.
Since the Connecticut shootings, the NRA has been taunted and criticized at length, vitriol that may have prompted the shuttering of its Facebook page just a day after the association boasted about reaching 1.7 million supporters on the social media network.
Twitter users have been relentless, protesting the organization with hashtags like NoWayNRA.
The NRA has not responded to them. Its last tweets, sent Friday, offered a chance to win an auto flashlight.
Offline, some 300 protesters gathered outside the NRA's lobbying headquarters on Capitol Hill on Monday chanting, "Shame on the NRA" and waving signs declaring "Kill the 2nd Amendment, Not Children" and "Protect Children, Not Guns."
"I had to be here," said Gayle Fleming, 65, a real estate agent from Arlington, Va., saying she was attending her first antigun rally. "These were 20 babies. I will be at every rally, will sign every letter, call every congressman going forward."
Retired attorney Kathleen Buffon of Chevy Chase, Md., reflected on earlier mass shootings, saying: "All of the other ones, they've been terrible. This is the last straw. These were children."
"The NRA has had a stranglehold on Congress," she added as she marched toward the NRA's unmarked office. "It's time to call them out."
The group's reach on Capitol Hill is wide as it wields its deep pockets to defeat lawmakers, many of them Democrats, who push for restrictions on gun ownership.
The NRA outspent its chief opponent by a 73-1 margin to lobby the outgoing Congress, according to the nonpartisan Sunlight Foundation, which tracks such spending. It spent more than 4,000 times its biggest opponents during the 2012 election.
In all, the group spent at least $24 million this election cycle — $16.8 million through its political action committee and nearly $7.5 million through its affiliated Institute for Legislative Action. Its chief foil, the Brady Campaign to Prevent Gun Violence, spent just $5,816.
On direct lobbying, the NRA also was mismatched. Through July 1, the NRA spent $4.4 million to lobby Congress to the Brady Campaign's $60,000.