Schattschneider on the Electoral College

"the success of the Democratic party in disenfranchising the Negro in the South has been due in part to the fact that the Republican party has given up the contest in these states as hopeless and unprofitable...
It is extremely doubtful if the monopoly of the white Democrats in the South could survive a series of determined attacks by an opposition party that did not need to get 50 plus per cent of the vote in any Southern state to make its invasion profitable.  Moreover, confronted by this renewal of party competition, the Democratic party probably could not afford to insist on the exclusion of the Negro from the franchise.  It might find itself competing for the Negro vote.  The main prop of the Solid South thus appears to be the electoral college."

(p122-123, "Party Government" by E.E. Schattschneider)