Check out this blast from the past. In a 1956 ad from National Comics, Superman tells a group of school children:
… and remember, boys and girls, your school—like our country—is made up of Americans of many different races, religions and national origins. So … if YOU hear anybody talk against a schoolmate or anyone else because of his religion, race or national origin—don’t wait: tell him THAT KIND OF TALK IS UN-AMERICAN.
Republicans (and some Democrats) today would do well to remember this.