Complex sentence: In 2013, Harold Hamm, CEO of Continental Resources, co-chaired Pruitt's reelection campaign; upon his re-election, Pruitt jointly filed a lawsuit against a federal regulation alongside the Oklahoma Gas & Electric and an energy industry group funded by Hamm.
Split into simpler sentences: In 2013, Harold Hamm, CEO of Continental Resources, co-chaired Pruitt's reelection campaign. Pruitt then jointly filed a lawsuit against a federal regulation alongside the Oklahoma Gas & Electric and an energy industry group funded by Hamm.