Why does Obama stutter when he don't have his teleprompter?

* when he doesn't have his teleprompter.

Because normal speech is much more difficult as it involves feedback and thinking rather than just reading something off a screen in a "mechanical" way

You stand up in front of 100 cameras, give a speech from memory, and tell me if you don't stutter or fumble.

Because he's a half way decent actor but doesn't have a cohesive thought in his head.