query: SELECT ?item ?party ?district ?start ?end ?cause WHERE {
    ?item p:P39 ?statement.
    ?statement ps:P31 wd:Q4164871;
      pq:P5054 wd:Q55435983.
    OPTIONAL { ?statement pq:P580 ?start. }
    OPTIONAL { ?statement pq:P582 ?end. }
    OPTIONAL { ?statement pq:P1534 ?cause. }