Complex sentence: The PCI expected Pertini to use his influence in their favour, but the President was influenced by other political leaders like Giovanni Spadolini of the Italian Republican Party and Bettino Craxi of the Italian Socialist Party; and thus the PCI remained out of the government.
Split into simpler sentences: The PCI expected Pertini to use his influence in their favour. But the President was influenced by other political leaders like Giovanni Spadolini of the Italian Republican Party and Bettino Craxi of the Italian Socialist Party, and the PCI remained out of the government.