U.S. is a republic, not a democracy

President Obama referred to our nation as a "democracy" several times during his Democratic National Convention speech. I guess he wasn't taught in grad school, nor was he teaching his students as a constitutional law professor, that our nation is not a democracy. We are a republic, Mr. President. There is a huge difference.
A republic has enumerated powers for the government and maximum freedom for the people. The enumerated powers ensure limited government. A democracy allows for mob rule by simply majority vote. A democracy allows for votes that diminish freedom and embolden tyranny. But perhaps Obama prefers the democratic labels to create more power for him and his cronies and less adherence to constitutional government?
David Thomas