No, President Obama should not use nuclear weapons upon Iran, nor should he use them anywhere else. Nuclear weapons produce so much wanton and reckless killing that they should never be used anywhere on Earth ever again. Whatever sins Iran may have commited as a nation, its people do not deserve such death and destruction.
Iran's missile capabilities don't threaten the United States, they threaten Israel and possibly Europe. President Obama shouldn't intervene in Iran whatsoever just because leaders in Israel claim there is a fictitious "red line" to be crossed. Now that Mahmoud Ahmadinejad is out of power, the west should soften its stance with Iran and try to negotiate for a peaceful nuclear deal. No one should be nuking someone else anymore, now that major powers have learned lessons from the Cold War.