CREATE TABLE table_21789 ("Poll Source" TEXT, "Dates administered" TEXT, "Democrat: John Lynch" TEXT, "Republican: Joe Kenney" TEXT, "Lead Margin" FLOAT)

Name the most lead margin for republican joe kenney being 23%
SELECT MAX("Lead Margin") FROM table_21789 WHERE "Republican: Joe Kenney" = '23%'
SELECT MAX("Lead Margin") FROM "table_21789" WHERE "Republican: Joe Kenney" = '23%'