@Pat494 brought up Nazis in relation to the conversation about Trump and Le Pen. I was pointing out that this is very common in illogical arguments, so much so that a psychological phenomenon exists around it. Once such a comparison is made, whoever mentioned the Nazis has automatically lost whatever debate was in progress. This principle is itself frequently referred to as Godwin's law. This came after Strauss's term reductio ad Hitlerum, which derives its meaning from reductio ad absurdum.
If Hitler liked neoclassical art, that means that classicism in every form is Nazi; if Hitler wanted to strengthen the German family, that makes the traditional family (and its defenders) Nazi; if Hitler spoke of the "nation" or the "folk," then any invocation of nationality, ethnicity, or even folkishness is Nazi ..."
It is still fallacious. Why bother making any arguments if you are not going to use and follow logic. The suggested rationale is one of guilt by association. This is where reductio ad absurdum comes in.
it is a tactic often used to derail arguments, because such comparisons tend to distract and anger the opponent, as Hitler and Nazism are seen as unpopular in the modern Western world.
Ducks are water-based, winged-birds; however, not all winged-birds are ducks and; thus, the argument falls apart there. Converse fallacy. Your statements only works forward not backwards. You are using the biconditional where only modus ponens works. You have stated the if P then Q, but you have disregarded any statements resembling the if Q then P to allow for a biconditional.
It is invalid if you invert the argument. If Trump walks like a duck (Wx) and quacks like a duck (Qx), then Trump is not necessarily a duck.
http://www.umsu.de/logik/trees/
\forallx(Dx\to(Qx\land Lx))\to(Dx\to(Qx\landLx))