The lesser of two evils voting behavior.
One of the most pernicious effects of "lesser of two evils" voting, beyond its obvious perpetuation of evil, is the fact that it turns adherents into partisans.
I can't tell you how many times I've watched people go from "X is evil but still better than Y" to "X actually isn't evil after all."
It's as if the mere act of casting your vote for someone forces you to start subconsciously polishing that person's record.
Somewhere along the way, "Obama did some evil things but I'll take him over Romney" turns into "the worst thing Obama ever did was wear a tan suit."
Humans have some funny psychological quirks... one of them being to "normalize" even their worst decision making. Whether it's politics, or agreeing to take an absolutely horrible job and then "defending" that action... it's pretty much everywhere.
=^..^=