Electromagnetic caterpillar drive.

Robert Zubrin researched the idea of using large electro-magnetic fields to produce drag against the sparse interstellar medium. Found it would be a feasible way of slowing down an interstellar spacecraft.

I'm wondering if a series of electromagetic fields switched on and off in a caterpillar like fashion could utilise this same drag to cause forward motion. Somewhat analogous to an ancient roman sea vessel except it would use electromagnetic fields stretching thousands of kilometres into space instead of oars. This is the second time I've tried to post this. My posts keep getting deleted but I'm never told why.