Complex sentence: The Anti-Defamation League (ADL) repeatedly challenged statements made by Piper, and called him a promoter of antisemitic conspiracy theories, a Holocaust denier, and a defender of the "Protocols of the Elders of Zion".
Split into simpler sentences: The Anti-Defamation League (ADL) has repeatedly challenged statements made by Piper. It calls him a promoter of antisemitic conspiracy theories, a Holocaust denier, and a defender of the "Protocols of the Elders of Zion".