WASHINGTON -- Some families who lost loved ones in December's massacre at a Connecticut elementary school expressed disgust and disappointment Sunday over the Senate's defeat last week of the most far-reaching gun control legislation in two decades, as they pledged to keep fighting for measures to prevent gun violence.

Neil Heslin, Erica Lafferty and Carlee Soto were among the Newtown, Connecticut, family members who spent a week on Capitol Hill describing how their loved ones died at Sandy Hook Elementary School on Dec. 14. But their stories of horror and heroism were no match for a threat from the National Rifle Association, the influential gun rights lobbying group, which led the opposition, and concern from Republicans and a small band of rural-state Democrats.

Lafferty, whose mother, school principal Dawn Hochsprung, lunged unarmed at the gunman to stop him from firing the assault weapon, said she was "honestly disgusted that there were so many senators that are doing nothing about the fact that my mom was gunned down in her elementary school, along with five other educators and 20 6- and 7-year-old children."

The Senate rejected on Wednesday a series of gun control bills that would have tightened background checks for buyers, banned assault weapons and high-capacity ammunition magazines, and loosened restrictions on carrying concealed weapons across state lines, the last measure backed by the NRA. The votes were a setback for President Barack Obama who had made gun control legislation a top priority of his second term after the Sandy Hook massacre.

The measure to tighten background checks to include online and gun show sales received 54 votes in the 100-seat Senate, but that fell short of the 60 votes needed under Senate procedural rules to advance the legislation to a final vote. Current federal law only requires background checks for gun purchases at licensed gun dealers.

Supporters of background checks maintain that it would make it more difficult for criminals and severely mentally ill people to obtain firearms. Opponents said the measure would be ineffective and could facilitate the creation of a national registry of gun owners, making it easier for the government to someday tax or confiscate firearms.

Within hours of the Senate votes, former Rep. Gabrielle Giffords accused senators who opposed the new regulations of "cowardice" in a piece published in the New York Times' op-ed page. Giffords was among 13 people wounded two years ago when a lone gunman opened fire as she met with constituents in a Tucson, Arizona, shopping mall, killing six others. She and her husband, retired astronaut Mark Kelly, had lobbied for the bills' passage.

On CBS' "Face the Nation," moderator Bob Schieffer asked Heslin, Lafferty and Soto Sunday whether the words "cowardice" and "cowards" were appropriate to describe Wednesday's vote.

"I do," said Heslin, who's 6-year-old son Neil Lewis died at Sandy Hook. "I feel they're not standing up for what they should be."

Carlee Soto, recounted her sister Victoria's courage to try to save her students, Neil Lewis among them.

"My sister wasn't a coward that day. My sister pushed the kids up against the wall, out of sight," she said, adding, "She protected her kids. Why aren't they protecting us?" referring to the senators who voted against the gun bills.

The families say the gun legislation would have strengthened laws already in effect rather than undercut the U.S. Constitution's Second Amendment, which guarantees the right to bear arms.

"It's beyond me how these congressmen cannot stand up and support something that would prevent -- or help prevent -- something like this from ever occurring again," Heslin said.

"We aren't going to go away. I know I'm not," he added. "We're not going to stop until there are changes that are made."