If parties in a republic are necessary to secure a degree of vigilance sufficient to keep the public functionaries within the bounds of law and duty, at that point their usefulness ends. Beyond that they become destructive of public virtue, the parent of a spirit antagonist to that of liberty, and eventually its inevitable conqueror.

Tocqueville, Alexis De. Democracy in America: The Complete and Unabridged Volumes I and II, translated by Henry Reeve. Bantam Classics, 2000, vol. 2, sect. 2, ch. 12.

Madison, James. "No. 51: How to maintain: make the parts check each other. Also, a federal system divides power further.--Madison (or Hamilton)." The Federalist: A Commentary on the Constitution of the United States, edited by Robert Scigliano. The Modern Library, 2001.

Churchill, Winston. "The Soviet Danger: The Iron Curtain." Blood, Toil, Tears and Sweat: The Great Speeches, edited by David Cannadine. Penguin Classics, 2007.