Complex sentence: MacDonald impressed the local press Dover Express, 17 June 1892; 12 August 1892 and the Association and, was adopted as its candidate; announcing that his candidature would be under a Labour Party banner.
Split into simpler sentences: MacDonald impressed the local press Dover Express, 17 June 1892; 12 August 1892 and the Association, however, and was adopted as its candidate. MacDonald, though, announced that his candidature would be under a Labour Party banner.