Intelligent Design proponents originally claimed that the flagellum was "irreducibly complex". But there are, in fact, a vast array of flagellum and flagellum pre-cursors evident in nature so it is clearly not irreducibly complex. This claim is one of the best examples of the flaw in the entire approach of Intelligent Design which would ask that you stop looking any further for a natural explanation when in fact, there is a tremendous amount of knowledge hiding behind understanding the TRUE origin of the flagellum.
The flagellum of E. coli contains 40 proteins but only 23 of these proteins are common to other bacterial flagella. Furthermore, many of these proteins server other functions in the cell. For example: the hole used by the flagellum existed prior to use by the flagellum as a protein export portal.
Evolution: Reducible Complexity — The Case for Bacterial Flagella" is just one of many scientific papers on the resolution to this question.
See also, 24 Evolution Myths and Misconceptions