What if I republish another person's statement? (i.e. someone comments on your posts)
Generally, anyone who repeats someone else's statements is just as responsible for their defamatory content as the original speaker—if they knew, or had reason to know, of the defamation. Recognizing the difficulty this would pose in the online world, Congress enacted Section 230 of the Communications Decency Act, which provides a strong protection against liability for Internet "intermediaries" who provide or republish speech by others. See the Section 230 FAQ for more.

The vast weight of authority has held that Section 230 precludes liability for an intermediary's distribution of defamation. While one California court had held that the federal law does not apply to an online distributor's liability in a defamation case, the case, Barrett v. Rosenthal, was overturned by the California Supreme Court (EFF filed an amicus brief in this case)

https://www.eff.org/issues/bloggers/legal/liability/defamation