Being a UK citizen I don't know the details of US politics but this should be an opportunity to take a step back and try to see through all the rhetoric, self serving and downright corruption in politics of any persuasion or nation.
You have to ask yourself has Barak Obama lived up to his pre-election promises or even any of them. Has he discharged himself in an honorable and honest way ? Has the USA prospered or become anymore secure under his leadership ? With the state of the world economy and security is he addressing the issues in a competent and statesmanlike manner ? Finally do you feel you can trust anything he says ?
If the answer to any of the questions is no then you must ask yourself if there is any of the other runners you could say this about.
If the US political situation is anything like that of the EU then your answer is almost certainly no.
The only consideration then open to you is to vote for the person you feel will do you and your country the least damage.
Kind regards and good luck Peter.