query: SELECT ?pres ?presLabel ?party ?partyLabel ?startdate ?enddate WHERE {
    ?pres wdt:P39 wd:Q13527950.
    OPTIONAL {
      ?pres p:P39 ?position_held_statement.
      ?position_held_statement ps:P39 wd:Q13527950.
      OPTIONAL {
        ?position_held_statement pq:P580 ?start.
        BIND(SUBSTR(STR(?start), 1, 10) AS ?startdate)
      }
      OPTIONAL {
        ?position_held_statement pq:P582 ?end.
        BIND(SUBSTR(STR(?end), 1, 10) AS ?enddate)
      }
    }
    OPTIONAL {  }
    OPTIONAL { ?pres wdt:P102 ?party. }
    SERVICE wikibase:label { bd:serviceParam wikibase:language "en". }
  }
  ORDER BY ?start
  