There is no enemy of free government more dangerous and none so insidious as the corruption of the electorate.
 Theodore Roosevelt, State of the Union Address. copy citation

Context

“I recommend that an examination be made into the subjects of citizenship, expatriation, and protection of Americans abroad, with a view to appropriate legislation. The power of the Government to protect the integrity of the elections of its own officials is inherent and has been recognized and affirmed by repeated declarations of the Supreme Court. There is no enemy of free government more dangerous and none so insidious as the corruption of the electorate. No one defends or excuses corruption, and it would seem to follow that none would oppose vigorous measures to eradicate it. I recommend the enactment of a law directed against bribery and corruption in Federal elections.” source