Rahm Emmanuel didn’t “criticize mentally challenged people”, he used “retards” as an insult, a very common thing that many of use have said. And he’s aimed his insult at liberals. He’s not a liberal; Emmanuel is very much a conservative.
Reid put his foot in his mouth: he said something that would have been considered enlightened back in the 1950s - a very common occurrence among older people (my own mother, who was an active anti-racist, used descriptions that would raise eyebrows nowadays, such as “he’s so articulate”). Reid also apologized for his choice of words. Plus you should consider his voting record on matters of civil rights.
Byrd? Are you kidding? He was a KKK member briefly in his youth (he’s in his 90s now), and has renounced, apologized for and washed his hands of that stage of his life. Since that time he has been one of the strongest defenders of the US constitution. Plus you should consider his voting record on matters of civil rights.
Right-wing apologists keep trying to draw equivalences between racism on the right and perceived “racism” on the left. There is no equivalence. Racism by definition is a right-wing trait, since it divides people into categories of “worthy” and “unworthy”, a central trait of right-wingerism; left-wingerism, on the other hand, sees all humans as equal. If a “liberal” is racist, he’s not a liberal.