You have two like charges with the same velocity and a displacement between them perpendicular to the velocity. Moving charges produce a magnetic field. The charges should magnetically attract one another. Now consider the reference frame of the charges. There is no motion so no magnetic field exist. How is this possible? The two charges exert a repulsive force on each other due to their electric field. How do these two forces relate to one another? The answer (if you can figure it out) might surprise you.