Obama won for three reasons:
- Better one liners: Obama had the more memorable moments and memorable lines. Highlights include "the 1980s called - they want their foreign policy back" and Obama chiding Romney by explaining in rudimentary terms how a modern navy works.
- Romney on defense: Unfortunately for Romney, many of his positions are similar to Obama with regards to foreign policy. This made it difficult for him to make too many contrasts with Obama, which given Obama's position as the President, makes it seem like Romney doesn't have any original ideas.
- Domestic policy is not the best fall back: in this debate, falling back to domestic policy makes it seem like Romney was going off topic and therefore either not focused or not knowledgeable enough about the topic at hand. Even if that penalty was not strong, Obama came out ready for domestic policy anyways, and giving him a second chance to avenge Denver is not strategic.
So in short, Obama won.