CREATE TABLE "table1_1958768_3" (
  "district" text,
  "vacator" text,
  "reason_for_change" text,
  "successor" text,
  "date_successor_seated" text
);

Question: Name the vacator for wisconsin 1st
SQL: SELECT "vacator" FROM "table1_1958768_3" WHERE "district"='Wisconsin 1st';

Question: Name the successor for pennsylvania 15th
SQL: SELECT "successor" FROM "table1_1958768_3" WHERE "district"='Pennsylvania 15th';