Documents reveal Eminem was actually visited by Secret Service for anti-Trump lyrics

Incorrect. An ad hominem fallacy refers to an argument which bases itself on assertions regarding the speaker when the subject of argumentation does not pertain to the speaker. But it does not follow from the fact that discussion of information regarding a speaker may in such circumstances be irrelevant to an argument (and therefore a red herring) that information regarding a speaker is inherently irrelevant to any discussion whatsoever.

If I say "I am the Queen of Spain", and you say "You are clearly not the Queen of Spain - first, you're not Spanish, and second you've never even been to Spain" you are not engaging in ad hominem. You are responding to an assertion with relevant and contradicting evidence. If I say, on the other hand, "the Spanish Civil War was an unnecessary and disastrous period of suffering for the Spanish nation" and you respond "first, you're not Spanish, second, you've never even been to Spain" you are engaging in ad hominem. Because the Spanish Civil War being the things described is in no way contingent on my being from or living in Spain.

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