Call your opponent a Nazi when you are actively using Nazi strategy.
Why? Just in case you are found out to be using such tactics, the person you have stigmatized first will have already taken the media hit for you and you can continue using the tactic in relative freedom.
Democrats are always yelling about Nazies. Bush was one, Cheney was, Condie, it’s lost it’s effect. The only American I can remember that saddled up to them was Old man Kennedy. He cuddled with the muzzies as well. That’s another group that’s fascinated a bout the Nazies.