If the Winter Soldier was responsible for the Kennedy assassination and Magneto tried to STOP the Kennedy assassination then that must mean somehow Magneto lost a fight to a guy wITH AN ENTirE ARm MADE OF METAL
Marvel writers sweat intensely
Maybe they made a wooden duplicate that was spraypainted chrome. magnetos mind would have been instantly destroyed when he couldnt control it and he would give up without any further attempt to do something.