On a sultry July morning, Cao, the first-term Republican congressman from New Orleans, walks out of his house in the Venetian Isles neighborhood in the easternmost part of the city, a low tentacle of land rising, just barely, above the waters of Bayou Sauvage. A dawn fog sits heavily over the adjacent swamp; a dead palm leans in memoriam to Hurricane Katrina (or maybe Gustav; both of them devastated his house).