that Congress intended that ???all changes, no matter how small, be subjected to ?? 5 scrutiny,????? id. at 568); see also City of Rome v. United States, 446 U.S. 156, 180???81 (1980) (finding that Congress recognized in 1975 the critical role that section 5 played in addressing discriminatory dilutive measures enacted after literacy tests and other barriers to black enfranchisement had been remo