CREATE TABLE table_56608 ("Congress" TEXT, "Bill number" TEXT, "Date introduced" TEXT, "Sponsor" TEXT, "# of cosponsors" FLOAT)

Who was the sponsor on April 22, 2004?
SELECT "Sponsor" FROM table_56608 WHERE "Date introduced" = 'april 22, 2004'
SELECT "Sponsor" FROM "table_56608" WHERE "Date introduced" = 'april 22, 2004'