Racism would not be an easy sell to a large audience in his time. The quest for civil rights legislation had been won by the early seventies. Unlike the executive and the judiciary, a legislature can tolerate a racist (or other extremist) here and there. Result: he could make the state senate. Duke's only chance to win a statewide election would be if the opponents fielded a corrupt idiot, not impossible in Louisiana. Even so, he would not last more than one term in the US senate.