Sen. Joe Manchin (D-W.Va.) said Thursday morning that the National Rifle Association "made a big mistake" by opposing his gun background checks compromise legislation, saying the amendment would have gotten 70 votes without the NRA's interference.

Manchin said he's not worried about the possibility that the NRA, which previously gave him an 'A' rating, will lower that rating because of the compromise he hammered out with Sen. Pat Toomey (R-Pa.). And then the senator, who once fired a rifle at climate change legislation in a campaign ad, took aim at the group's tactics.

"I think they made a big mistake," Manchin said at a breakfast hosted by The Wall Street Journal. "I hope that they are able to look at the mistake they made and look at the bill for the facts that's in it and say, fine, we gotta let our members vote and not score the next time we come -- I would love to see that happen."

Manchin also echoed President Obama, who on Wednesday accused the NRA and other gun groups of lying about the Manchin-Toomey amendment's effects. Manchin called their claims "ludicrous."

"When they put the quotes they put in there -- that's not true," he said, referring to the NRA's claims about how the legislation would affect gun sales between family members.

"I guess (it would matter) if you're going to sell your sister a gun on eBay," he said. "I would check your relation with your sister before you do that, because something's falling apart."