Jump on the band rail

“Jump on the bandwagon” (to voluntarily participate in something) is what the speaker meant to say, but apparently was derailed in his thinking and confused his train of thought.  As “my ol pal” points out, years ago politicians (e.g Truman) used to have whistle-stop campaigns where the candidate would ride aboard a special train & make stops in various places so that the public could see them, hoping that the voters would “jump on their bandwagon.”  So, perhpas the phrase “riding the rails” (hobos getting free rides on the trains) was probably the source of the confusion, with the speaker thinking about railroads instead of wagons, both forms of transportation.  Finally, to “jump the rails” (train goes off the track) might be the missing idiom as it contains the word “jump” even though the thought is opposite to jump ON the bandwagon.  The subconscious is indeed a mystery….