CREATE TABLE "table1_2417390_4" (
  "district" text,
  "vacator" text,
  "reason_for_change" text,
  "successor" text,
  "date_successor_seated" text
);

Question: What district was the successor seated in March 28, 1878?
SQL: SELECT "district" FROM "table1_2417390_4" WHERE "date_successor_seated"='March 28, 1878';

Question: Who was the vacator for the district of Nebraska at-large?
SQL: SELECT "vacator" FROM "table1_2417390_4" WHERE "district"='Nebraska At-large';