Apparently if the White House or any other place Obama will frequently visit happen to be under fire or under a threat he'll just have to run to his limo.
6.5-litres is pretty big and keep in mind that torque is a lot more important since this car uses GMC's TopKick truck platform as it's base chassis and will easily weigh in over three tons considering everything packed in the car. A 6.5-litre diesel engine should be more than enough to get Cadillac One (or "The Beast" if you're the Secret Service) moving.
Some body was watching the History Channel last night. They had a couple of programs on that took some close looks at Air Force 1 and the limo. With in security limits of course. But it was interesting to say the least.