CREATE TABLE table_75765 ("Date" TEXT, "Tournament" TEXT, "Winning score" TEXT, "Margin of victory" TEXT, "Runner ( s ) -up" TEXT)

Which Margin of victory has a Tournament of u.s. senior open?
SELECT "Margin of victory" FROM table_75765 WHERE "Tournament" = 'u.s. senior open'
SELECT "Margin of victory" FROM "table_75765" WHERE "Tournament" = 'u.s. senior open'