Complex sentence: He subsequently joined the New Democratic Party, becoming its first ever Quebec Member of Parliament (MP), but left the party after ten months to again sit as an Independent, after claiming that communists had infiltrated the party.
Split into simpler sentences: He subsequently joined the New Democratic Party, becoming the first NDP Member of Parliament (MP) from a Quebec riding. However, he left the party after ten months to again sit as an Independent, after claiming that communists had infiltrated the party.