Bruce Raynor’s argument (letter, “Prejudgment? Take a look in the mirror.”) commits the “tu quoque” fallacy. It is a logical error of relevance.
Whether Democrats are prejudiced is irrelevant to the positive claim of prejudice by Senate Republicans.
If I am a liar, and you lied, and if I were to call you a liar, then it wouldn’t do to rebut my claim by pointing out that I’m a liar.
You can still lie and be correctly called a liar — by liars and non-liars alike. So, Mr. Raynor has not defeated the positive assertion that “Senate Republicans have failed in their sworn commitment to impartial justice.”