They didn't lose. You're probably talking about Nazi Germany. Yes, that country lost. Doesn't mean Nazis in Germany magically disappeared. Doesn't mean Nazis anywhere else disappeared. Your dad never won over Nazis, just one particular Nazi country.
The Nazi party fled to many corners of the globe. Fascism exists outside of the Nazi party. Between those two things, fascism never really died. The Nazi party was shut down, made illegal in much of Europe. The other fascists welcomed those that made it out. Most modern day fascists that use Nazi imagery are called neo-nazis. Not the same group from WW2. Neo-nazis have been around for decades. Until recently they were not nearly as organized.
Get a photo of his ugly mug. Get an old, cheap laser printer. I recommend a Kyocera fs-3900 or something similar because the toner can be found cheap. Print out rumors, gossip, lies. Post them all over the neighborhood. Let the community know he is a Nazi (if that will help)