It's quite simple really -- you upset the status quo.
For one, you're a "Black man." Nobody is outright playing the race card, but then no one would be stupid enough to. And yet you know that behind closed doors in America, there are people actually frightened at the thought of you holding the reins. Their fear is that there will some kind of retribution for slavery or there will be rioting in the streets as your brethren decide to "punish the White man." It's frightening that living in an age of information as we do, such parochial views are still widespread.
For another, you're a Democrat. Yes, the mere fact that you are not of the party in power has them worried, at least those who have been making out quite well living off of other people's money and resources. The "fat cats" have been having a party for 8 years and they are afraid that the chips and dip are gone, the bar is closing, and they will soon have to stumble blearily back to the cloakroom. The idea that very soon they might actually be forced to fork over some of their money to foot the bill for the extravaganza has them spooked.
And further still, you are a progressive. You want to change how our federal government operates. You want to take away the pacifier that is oil and replace it with renewable energy. You want Congress to stop handing out candy (earmarks) to the States. You want everyone, everyone, to be able to go to the doctor or the hospital when they need to. And what you want everyone's kids to have a level playing field when it comes to education. You're threatening to upset the balance of power, to tear down class distinctions and remove the things that separate "us" from "them." In essence, you want to change the structure of society, and that will not do.
And you're upbringing leaves a lot to be desired. No nuclear family, in a suburb, with a white picket fence around the house and church every Sunday. Raised by a single mother and your grandparents -- who are you kidding! That does not make a family! Exposing children to other cultures and belief systems, confusing them with different ideas. What was your mother thinking?
And to top it off, you're a smart man. The smart kids are the ones who get picked on in high school. They're usually the kids with little money, no fancy stuff to wear, a simple life that affords them the time to learn and grow. They are not supposed to be successful, only to supply those who are successful with grist for the mill. There can be no working your way up the food chain -- you have to be invited up to the heights. We can't have people getting the idea that yes, anyone can be President. That will never do, or the next thing you know, Washington, D.C. will be filling up with people who shun special interests and are not susceptible to graft and blackmail, who want to work for the common good.
Yes, Senator Obama, you scare some people. Not me, because your life resonates with mine in many ways and because you seem to hold the promise of the future out as a reality, something I have always striven for. No, you scare those people who are used to things being "the way they are" and don't care much for progressive social thinking. Those are the people you have to convince if you are to succeed; not many, but enough of those who are sitting on the fence to tip the balance. You've got to show them that their world will change but it will be good change and won't mean the end of their way of life. Do that, and this election is in the bag.