Complex sentence: He initially supported the policies of President James Polk and, representing the agrarian nature of his district, voted for the Walker Tariff of 1846 which created a moderate decrease in tariff rates.
Split into simpler sentences: He initially supported the policies of President James Polk. Also, as a Representative of a largely agrarian district, he voted for the Walker Tariff of 1846 which made a moderate reduction in tariff rates.