"Sadly, what I’m going to have tell them is the NRA won again," he said.

Still, Democrats were not able to describe a path forward, and had to explain how they would succeed in winning over more than a dozen Republicans when they lost Heitkamp on both of their bills and also lost Manchin and Tester, the head of the Senate Democrats' campaign committee, on the bid to tighten background checks.

“We should keep the focus on the Republicans. We’re doing our job. Democrats are doing our job," said Reid. “Republicans are just about as phony as anyone can be. All they care about is taking care of the NRA.”

Sen. Dianne Feinstein (D-Calif.), who wrote the bill aimed at potential terrorists, suggested the only way change might come was at the ballot box.

"I'm hoping that one day, the climate will change," she said. "We're going into an election season, and Mr. and Mrs. America, you have to stand up, and I'm going to vote only for people who will do something to close the terror gap, to keep guns out of the hands of people who are mentally incompetent, who are criminals and would use them illegally. Maybe, just maybe, this next election can produce something."

It was unclear how the Senate would act next. Sen. Susan Collins (R-Maine) had promised to bring forth a compromise measure on the terrorist watch list amendment that would use a more narrowly focused set of watch lists, but Democrats said they had yet to see it.

The NRA came to the defense of Republicans, calling the Democratic attempts to close loopholes an "embarrassing display."

“We all agree that terrorists should not be allowed to purchase or possess firearms. We should all agree that law-abiding Americans who are wrongly put on a secret government list should not be denied their constitutional right to due process," said Chris Cox, the head of the NRA's lobbying and political campaign wing, referring to concerns that there are people on various watch lists when they shouldn't be. "It is shocking that the safety of the American people is taking a backseat to political theatre."

This story has been updated to include comments from Feinstein, Reid, Nelson and the NRA.