Per the email quoted in the indictment, the Gun Rights Organization is referred to as "the largest sponsor of elections to the US Congress, as well as a sponsor of The CPAC conference [...]".
NRA's been linked to Russian funding already, too
https://www.politico.com/story/2018/04/11/nra-russia-money-guns-516804
Too bad about scumbags in both parties Republicans' repeated efforts to block any sort of legislation requiring full disclosure of that sort of funding, though.