isn't failure to carry out one's mandated duties an impeachable offense?
It may be unethical, and is grounds for ejection from the body, but when a majority of the Senate is in the conspiracy, it ain't gonna happen. (Article I, Section 5 of the United States Constitution provides that "Each House [of Congress] may determine the Rules of its proceedings, punish its members for disorderly behavior, and, with the concurrence of two-thirds, expel a member.") Such are the perils of an ultra-partisan political environment.