Table: congress_changes_2
Columns: district
vacator
reason_for_change
successor
date_successor_seated

Question: What district was the successor seated in March 28, 1878?
SQL: SELECT "district" FROM congress_changes_2 WHERE "date_successor_seated" = 'March 28, 1878'

Question: Who was the vacator for the district of Nebraska at-large?
SQL: SELECT "vacator" FROM congress_changes_2 WHERE "district" = 'Nebraska At-large'