Mr. Gottlieb said that despite claims to the contrary, the amendment that would expand checks to sales online and at gun shows is “not registration” and went on to list a host of gun-rights protections in the measure, such as allowing interstate handgun sales for dealers and protections for veterans, for example.

“It’s a Christmas tree,” Mr. Gottlieb said. “We just hung a million ornaments on it.”

“We’re taking the background check and making it a pro-gun bill,” he added. “Unfortunately, some of my colleagues haven’t quite figured it out yet because they weren’t sitting in the room writing it,” he continued. “My staff was. I’ll be perfectly candid about it. This will probably break on Monday in the Wall Street Journal.”

“If you really read what’s in the Manchin-Toomey bill — man, it’s a godsend,” he went on to say. “We win rights back like crazy.”