The Center for Immigration Studies' lawsuit is devoid of any allegation that the law center made a false statement about the Washington-based nonprofit, U.S. District Judge Amy Berman Jackson in Washington, D.C., said in her ruling Friday.

"The upshot of the complaint is that defendants advanced a conclusion that was debatable, and that this expression of a flawed opinion harmed plaintiff's reputation," Jackson wrote.

The research group accused the Montgomery, Alabama-based law center's leaders of conspiring to violate the Racketeer Influenced and Corrupt Organizations Act when they designated it as a hate group in 2016. The judge, however, said the suit improperly attempts to "shoehorn" a defamation claim into the framework of a RICO case.