Question: to throw someone under the bus

Where does the expression to "throw someone under the bus" come from, meaning to double-cross someone? For that matter, where does "double-cross" come from?
The earliest I've been to trace the term with certainty is 1991, which I did in this entry in my online dictionary. You'll also see a 1984 citation there which alludes to a Cyndi Lauper concert tour and contains a reference to the term that could be related, but might not be. That citation has been widely misunderstood to be the earliest usage, both by William Safire, who quotes Paul Dickson and who in turn attributes the lines as if Cyndi Lauper herself said them, which she did not. Newsweek, in its turn, credits the 1984 “find†to Safire and doesn't mention Dickson. But it's wrong. 1991 is the earliest in-print use for the term that's been found so far.
Grant,
Your online dictionary reference seems only to be underlined--i.e. it is not a clickable web link. The Safire link works.
BTW, for our math-challenged fellows: Keep Trying; the "Save New Post" button comes live with the correct answer.
Emmett

Not sure of the origin of double cross, but I will relate a nice piece of trivia - the Twenty Committee of MI5 oversaw the use of 'turned' German spies in WW2. Twenty in Roman numerals is XX - a double cross. A wry sense of humour at work!
Chris
Ooo, didn't know that, Chris. Thanks!