Liberals put their faith in people – if we just have the right people in government (like Obama), everything will be grand. But the Founders designed our Constitution with the philosophy that power corrupts. From the Federalist Papers:
Power controlled or abridged is almost always the rival and enemy of that power by which it is controlled or abridged. This simple proposition will teach us how little reason there is to expect that the persons intrusted with the administration of the affairs of the particular members of a confederacy
will at all times be ready with perfect good humor and an unbiased regard to the public weal to execute the resolutions or decrees of the general authority. The reverse of this results from the constitution of man.
– Hamilton, Number 15