It's a pun on the word 'crooked'. The two main meanings are (1) twisted out of shape or position; (2) (informal) dishonest or illegal. In the film, he has a problem with his back - it is twisted out of shape. Most people (native english speaking ones, anyway :)) think politicians are dishonest. The line is funny (and clever) because it juxtaposes the different senses of this word. So it shouldn't really make sense but it does. Do you get it, now? And do you think it's funny :)

"Crooked" has two meanings: 1. 曲 2. 偏斜

haha When I read your question Bush immediately came to mind. :P

Politicians are considered liars and crooks in many countries.