CREATE TABLE table_27438 ("City" TEXT, "Population" FLOAT, "Registered voters" TEXT, "Democratic" TEXT, "Republican" TEXT, "D\\u2013R spread" TEXT, "Other" TEXT, "No party preference" TEXT)

If the registered voters is 66.8%, what is the minimum population?
SELECT MIN("Population") FROM table_27438 WHERE "Registered voters" = '66.8%'
SELECT MIN("Population") FROM "table_27438" WHERE "Registered voters" = '66.8%'