I think an Obama presidency would be a nightmare but not in the typical cataclysmic way. Let me say right off the bat that with Obama as president, we would see all bad situations made worse (ie. the economy, immigration, social policy) and dangerous situations made more dangerous (ie. nuclear armed Iran, arab terrorism, homeland security). But while Obama will certainly exacerbate existing problems, I have my doubt that America, Israel, or western civilization will collapse at a single cataclysmic event that was made possible by an Obama presidency. The image of 1984 (that of a boot stomping on a human face forever, big brother, willful slavery) doesn't seem as realistic as the picture painted by Brave New World.
The late communications theorist Neil Postman wrote in his "Amusing Ourselves to Death", that a 1984-like scenario will not be necessary for governmental tyranny. Freedoms will be discarded willingly. This will happen because people will be consumed by their consumption of trivia, America's greatest export. That this election may be won by Oprah, Matt Damon, George Clooney and their ilk, is indicative of how obsessed the American public have become with celebrity and with trivia.
Also, people don't read much these days. They watch television (which is an informationless medium, that can only stimulate and never educate) or browse the internet (for more trivia).
Obama will make it easy for people to not have to think so much. Unfortunately, I believe that is what most Americans want. We may come to a point where if we feel depressed, we only need to take a pill, and not have to bother scrutinizing our lives for meaning. Once we reach that point, I don't think that there will be much hope for us.