>>do you think the union should then go to bat for that employee? I think the union should absolutely have the right to pick and choose which cases to defend, especially in cases of clear and blatant violation of established rules and protocols.

Supreme Court decided long ago that unions are legally obligated to defend all of their members regardless of what they do. It is commonly referred to as the "duty of fair representation." It originated in Steele v. Louisville and Nashville Railroad, but there has been more than sixty years of jurisprudence extending and clarifying that right since then. Essentially, what it comes down to is that if you are a member of a union, and you do something dumb, the union has to defend you.