Unfortunately he said it in an interview about 3 weeks ago on Fox News.
Well in fairness he didn't actually compare anything to Nazis. He compared something to one single precept that was espoused and made well-known by them. Unlike say the "Punch a Nazi" movement from last year that literally claimed modern day Nazis are numerous and living amongst us.
Both the left and right do this, and it's almost never meaningful. More a lazy way to call your opponents poopheads.