Sen. Mike Lee (R-Utah), one of the original senators who threatened to filibuster gun-control legislation, said he’ll be voting against a compromise on background checks because of fear of what it could lead to.

Support for that legislative block fell apart Thursday when the Majority Leader Harry Reid (D-Nev.) received eight more votes than needed to move his gun bill forward to debate. The first amendment expected this week is the background-checks compromise between Sens. Pat Toomey (R-Pa.) and Joe Manchin (D-W.Va.).

“Toomey-Manchin does contain some carve-outs. But we know that today’s carve-outs are tomorrow’s loopholes and that’s of concern to us,” Lee said this morning on NBC’s Meet the Press. “This bill, I believe, would do more to limit the rights of the law-abiding than it would to actually prevent violent crime. And that’s why I can’t support it.”

GOP Sens. Mark Kirk (Ill.) and Susan Collins (Maine) are expected to support the amendment. Democratic Sens. Mark Pryor (Ark.) and Mark Begich (Alaska) voted against cloture on the gun bill and may vote against the amendment. Some Dems may object to a lack of universal background checks as sought and vote down the amendment, but most seem to be grudgingly down as yes votes.

“It remains to be seen whether it can pass the Senate,” Lee said.

“Following the tragedy at Sandy Hook, Americans have been rightfully focused on how to prevent such tragedies from occurring in the future,” he added. “But, unfortunately, the proposals we’ve seen would serve primarily to limit the rights of law-abiding citizens while doing little, if anything, to actually prevent tragedies like this from occurring in the future.”

Sen. Kirsten Gillibrand (D-N.Y.), on the show with Lee, disagreed, saying “there is so much in these bills that have nothing to do with law-abiding citizens.”

“You’re not undermining Second Amendment rights by saying criminals have to go through a background check before they can buy that weapon,” she said. “This is not about the NRA. This is about families. This is about America.”

Toomey and Manchin also took to the Sunday shows together to push their legislation. “If you’re a law-abiding gun owner, you’re going to like this bill,” Manchin said on CBS’ Face the Nation. “…Now, if you are a criminal or if you have been mentally adjudicated and you go to a gun show or try to buy a gun online, you might not like this bill because you can’t do it.”

Toomey said he believes his effort has been an uphill climb “because people have misconceptions about what’s in this bill, what it does.”

“For instance, they think there’s this whole new system that we’re created that they have reason to worry about. In fact, we’re just working with an existing system, the existing background system that some states have chosen not to provide much information,” he said. “In the case of the Virginia Tech shooting, for instance, that individual was — had been adjudicated as dangerously mentally ill. The court system in Virginia knew that, but the state never provided the system to the background check, so when he went to buy a gun he passed the test.”

“Under our bill we create greater incentives for states to provide this kind information, so hopefully they will and someone like him might be denied in the future,” Toomey added.

“This is not universal, let me be very clear, this is a criminal and mental background check bill only at gun shows and internet sales,” Manchin said. “…And you know we’re not infringing on people`s rights. We’re just not infringing on their rights. And a law-abiding gun owner — I come from a gun culture state of West Virginia.”

Sen. Marco Rubio (R-Fla.) indicated Sunday that the amendment is a non-starter for him, saying “criminals don’t care about the laws that we pass with regards to guns.”

“The problem is that all of these laws that people are discussing will not effectively deal with that problem, but will infringe on the Second Amendment rights of law-abiding citizens,” he said on ABC.

“No one is focusing on why this society has become so violent. Why young people in America are committing these horrifying acts,” Rubio added. “And we are missing a golden opportunity to discuss that, and not simply just focus on gun laws that only law-abiding people will follow?”