Complex sentence: To the surprise of many, Decore stepped down as Liberal leader not long after the election, supposedly under pressure from party insiders who were unhappy to find themselves on opposition benches and who felt that he missed the chance to form the government.
Split into simpler sentences: To the surprise of many, Decore stepped down as Liberal leader not long after the election. He was supposedly under pressure from party insiders, who were unhappy to find themselves on opposition benches, and who felt that he missed the chance to form the government.