Here's why I get concerned when Obama deals with Iran from a position of weakness.
The big issue here is not a nuclear threat to the US. It's a nuclear threat to Israel. Israel knows its national survival is at stake, and cannot afford to risk a nuclear Iran -- especially given Ahmadinejad's rhetoric about wiping Israel off the map in terms involving fire.
Israel also has a history of demonstrating that it will not accept such a threat. In 1981, they launched a daring long-distance raid that destroyed Iraq's Osirak nuclear reactor -- and Saddam at the time wasn't being near as beligerant towards Israel as Ahmadinejad is now.
Israel is counting on the US and the world to dismantle Iran's program. But their patience has limits. How do you think Obama is going to respond when Israel uses American aircraft to destroy Iran's nuclear facilities? Now is not the time to be naiive and indecisive -- he can make tough choices now, or make even tougher ones in the future.