CREATE TABLE table_21787 ("Poll Source" TEXT, "Dates administered" TEXT, "Democrat: John Lynch" TEXT, "Republican: Joe Kenney" TEXT, "Lead Margin" FLOAT)

Name the poll source for republican joe kenney being 28%
SELECT "Poll Source" FROM table_21787 WHERE "Republican: Joe Kenney" = '28%'
SELECT "Poll Source" FROM "table_21787" WHERE "Republican: Joe Kenney" = '28%'