Complex sentence: King and Conservative leader Arthur Meighen sparred bitterly in Commons debates, and the decades-long rivalry between the two was among the nastiest in the history of Canadian politics.
Split into simpler sentences: King and Conservative leader Arthur Meighen sparred constantly and bitterly in Commons debates. Dawson (1958) ch 14,15 The decades-long rivalry between the two was probably the nastiest in the history of Canadian politics.