Complex sentence: Mystery surrounded his actions for some years until it was discovered that he had fathered a daughter born in August 1916 to Winifred McNab and he because of a fear that this would become a public scandal during the election campaign.
Split into simpler sentences: Mystery surrounded his actions for some years until it was discovered that he had fathered a daughter born in August 1916 to Winifred McNab. He feared that this would become a public scandal during the election campaign.