Why should I fear Obama is my president and what is the worst a president can do?

I did not vote for Obama but please, Obama supporters, please give this question a chance you might find this interesting. Ok well we have all heard the none sense of Obama being the Antichrist and a muslim terrorist or what have you. But what are some REAL reasons as to why I should fear Obama. And what is the worst a president could do? From a political stand point even if Obama was hell bent on taking over the world (which I know is just dumb) does a president actually have the power to do such things? If a president was focused on ruining our nation is it actually within his power? What is the worst outcome of a horrible president? And for Obama haters please tell me what with his political background I should fear him. With his background and are just looking a difference in religious beliefs (like gay marriage, stem cell) or a real economic downfall/ I am looking for really informed political answers. And Obama supporters please list your thoughts and what is the worst A president can do (not meaning Obama)