Obama knows full well if Iran is allowed to get nukes it will spark a regional arms race which will result in Saudi Arabia and possibly Egypt & Turkey all developing their own nuclear weapons programs to counter the Iranian threat which he can't allow. He also knows its just a matter of time before Iran develops a missile with the range to hit mainland America and he doesn't want Iranian nukes pointed at Washington. So wait till December when the November election is out the way but before the swearing in of the next president in January. The US are the only ones with the hardware and range to do the job properly. The US fly undetected and bomb Iranian missile sites with their stealth B2 bombers which will limit Iranian retaliation capabilities. They can sink the Iranian ships and airbases just turn the entire Iranian military machine into scrap metal and of course total destruction of all Iran's nuclear facilities. Even if Israel was the one who tried to attack Iranian nuclear sites Iran would attack the US assets in the Gulf as well so best to make sure the people who can do the job best are the ones to start & finish the operation and if there is any role for Israel to play it will be to launch a single missile or send a handful of jets to provoke Iran into an attack and Obama can then say America is going to aid a friend or if Iran attacks an American airbase then its a declaration of war against America itself. Iran won't have a white christmas they will have an explosive one with bombs fall out the sky instead of snowflakes.
Trump: Middle East would be more stable if Saddam, Gaddafi still in power (Reuters)
from the article: Iran: U.S., Israel highly vulnerable to retaliatory strikes