CREATE TABLE table_72954 ("District" CLOB, "Incumbent" CLOB, "Party" CLOB, "First elected" FLOAT, "Results" CLOB, "Candidates" CLOB)

What district first elected a Democratic incumbent in 1998?
SELECT "District" FROM table_72954 WHERE "Party" = 'Democratic' AND "First elected" = '1998'
SELECT "District" FROM "table_72954" WHERE "First elected" = '1998' AND "Party" = 'Democratic'