It is hard to know for sure what drives President Obama and other U.S. officials. Below are four articles. The first is an important column by five former ambassadors to Iran from European nations. In this June 2011 column, they give their perspective about the cause of the stalemate in negotiations. They also point out that Iran is not in breach of international law.
The next four articles examine the tough U.S. approach to the recent negotiations in Baghdad between Iran and the P5+1 nations. The authors don't think that the U.S. is necessarily interested in reaching a negotiated settlement unless it is one that represents total Iranian capitulation.
The final reference here refers to the U.S. approach to diplomacy and the counterproductive imposition of sanctions.