Complex sentence: Melkert returned to the House of Representatives on July 13,1998 and became the Parliamentary leader of the Labour Party in the House of Representatives on July 13,1998 and became the presumed de facto next party leader in all but name.
Split into simpler sentences: Melkert returned to the House of Representatives on July 13,1998 and became the Parliamentary leader of the Labour Party in the House of Representatives on July 13,1998. And became the presumed de facto next Party leader in all but name.