In the aftermath of the twin defeats, Bloomberg's group and its allies were explaining the results by emphasizing local factors, including vote-by-mail limitations and particulars about these two districts. Both elections were decided by a tiny sliver of voters -- Giron lost the more lopsided race, by some 4,000 votes -- and their opponents were able to flood pockets of the state with cheap ads because only two senators had their jobs on the line.
"Full speed ahead," Mark Glaze, executive director of Mayors Against Illegal Guns, told ABC News on Wednesday. "The lesson of yesterday is one we already knew: You can cherry-pick elections, spend a lot of money, and defeat and elect candidates. We will do exactly the same."
Glaze noted that the new gun laws will remain in effect in Colorado, potentially saving lives. His group -- along with the more-established Brady Campaign to Prevent Gun Violence and the relatively new Americans for Responsible Solutions, started by former Rep. Gabrielle Giffords and her husband -- were providing an effective counter to the NRA's muscle, he said.
"The NRA, for two decades, was the only player in contests," Glaze said. "No one would show up to defend legislators, to protect the public. Now, lots of states are passing background-check laws and saving lives and living to tell the tale. The country has reached the tipping point, and there is now a counterpoint to the NRA."
Still, efforts at the federal level are stalled, if not stopped entirely. In April, the Senate rejected a pared-down bill expanding background checks, despite a bipartisan compromise that was being championed by the White House.
"This was a pretty shameful day in Washington," a visibly angry President Obama said in the aftermath. "If this Congress refuses to listen to the American people ... then the real impact is going to have to come from the voters."
That's, in part, what makes Tuesday's results problematic for backers of gun control. They learned again that for all the emotions such issues can stir, people on the other side of the issue are more motivated to do something about it at the ballot box.
A Pew Research Center survey from May found that nearly half of gun owners see gun policy as an important voting issue, compared to just one-third of those who live in households without guns. Gun owners are also more likely to say they wouldn't vote for candidates who don't share their views on gun control.
Families of gun victims aren't giving up hope. They're seizing their latest lobbying opportunity next week, when a Senate panel convenes a hearing about controversial "stand your ground" laws that came to light during the George Zimmerman trial.
Third Way's Bennett said the recall results showed the importance of careful messaging. Voters in Colorado largely approve of the new background checks, he said, but the ammunition limits were easier to run campaigns against.
"People hated the magazine ban, but they really liked background checks," he said. "In the context of the congressional debate, there is some comfort there, even for folks in purplish states."
But with the congressional agenda getting more crowded by the day, the latest setback was difficult to digest for backers of gun control.
"It's been real hard to get any oxygen around here for anything," Bennett said.
ABC News' Nicole Rossoll and Joan Greve contributed to this report.