demoralize

To destroy the morale of; to dishearten.

To erode the moral adherence of; to corrupt.

[I]f you convert a man brought up in another creed, you inevitably demoralize him.

The election of a man like Mr. Blaine would be such an encouragement to the base and rapacious impulses apt to govern the conduct of politicians, it would so demoralize the public mind and open the floodgates of corruption so wide, that it is no exaggeration to say the success of our free institutions is at stake.