The February filibuster of Chuck Hagel was the last straw for Harry Reid.
In the eyes of the Democratic majority leader, Republicans had just shattered a mere three-weeks-old agreement to avoid a drastic change to the Senate rules. Not only was the Hagel vote the first time in U.S. history the Senate filibustered a nominee to be secretary of defense, but the minority party took an unprecedented step and rebuked one of their own: Hagel was a former red state Republican senator who also happened to be a decorated war veteran.
This is a companion discussion topic for the original entry at https://talkingpointsmemo.com/?p=208378