Where does the phrase thrown under a bus come from?

One phrase that I notice on reality shows a lot is "thrown under a bus." The first time I heard it, I thought the contestant needed a Chicago accident attorney. It's another way of saying that you were stabbed in the back. If you are on a reality tv show you don't need to think of your own sentences anymore. Just say so & so threw me under the bus over & over.

I came across this article about the phrase last summer. However, I didn't read it until now because it's about a billion words long. It's interesting, just not as funny as I thought it should be. So, if you figure out where the phrase comes from, please let me know. I'd really like to throw it under the bus.