If you had a serious medical condition, whom would you ask for help? Would it be a plumber, a mechanic, a grocery clerk? While you might discuss your problems with them, you would seek definitive help from an expert, wouldn’t you?
In almost every circumstance, the best advice comes from experts in that field. That is why courts give credence to experts and their educated opinion. That is why you call a certified plumber if you have a leaky pipe, or an auto mechanic for the knocks in your car.
However, I have yet to see any field or endeavor where Senator Obama is recognized as an authority. Why? He simply is too young to have had enough time to become an expert. He has tried community relations for a few years. He has tried being a Senator for a few months. And, suddenly, he believes he is ready to be President of the United States!!!
He might consider himself ready, and he is definitely a smooth operator. But, most of us prefer someone tried and true, like Senator McCain.