Complex sentence: In addition, Cleveland's position on the tariff issue was unclear--thus allowing him to appeal to both high tariff supporters and low tariff supporters--and the fact that he was from a swing state (New York) further strengthened Cleveland's appeal among Democrats.
Split into simpler sentences: In addition, Cleveland's position on the tariff issue was unclear--thus allowing him to appeal to both high tariff supporters and low tariff supporters. Plus, the fact that he was from a swing state (New York) further strengthened Cleveland's appeal among Democrats.