Complex sentence: McKinley was disliked by the American Protective Association, an anti-Catholic group angered that he had appointed members of that faith as governor; their wide pamphleting cansed Hanna to act against falsehoods that his candidate was a Catholic.
Split into simpler sentences: McKinley was disliked by the American Protective Association, an anti-Catholic group angered that as governor he had appointed to office members of that faith. Their wide pamphleting cansed Hanna to act against falsehoods that his candidate was a Catholic.