Obama didn't just take out Osama...he's taken out al-Awlaki and about 20 other high value AQ operatives. He's gotten the job done, whereas the last republican administration didn't do jack shit other than waste billions of taxpayers dollars to enrich Chaney, Halliburton, and Blackwater.
Obama doesn't need to take out Iran's nukes, because they are no more of a threat to America's security than Saddam was. Israel has nukes and a well armed military, thanks to the American taxpayers. Let them go to war with Iran if they are so scared of a nuclear armed Iran!
Obama didnt kill any of them, US intelligence found them with the cooperation of foreign countries, and US special forces killed them in many cases, only thing Obama did was give the OK for the op.
Obama just had the luck of being the president sitting in office when the US agencies located him, nothing more, nothing less.
Giving him credit for killing those high value targets is akin to giving him credit for his favorite college football team winning their bowl game.

His foreign policy didnt kill them, they were already being hunted and he just gave the nod.
Thats all.