all of the major civil rights legislation of the 1960s was passed by a bipartisan coalition of republicans and northern democrats. support of civil rights by the democratic party leadership and by presidents kennedy and johnson essestially cost the democratic party its entire southern base (which is apparent from surverying the electoral maps post-johnson - only southern democrats carter and clinton have done even moderately well in the south). "the solid south" now votes solidly republican.
i'm not attributing that shift to a party realignment on that one issue alone - but it has played a part, sadly and to the gop's discredit.