I caught part of an interview with Tom Daschle earlier today. He was asked what he thought of the idea of going to war with Iraq. He said that now wasn't the time, that it would have unfortunate consequences that he wasn't sure we could endure. (This is from memory, so it's not an exact quote. But it's the gist of what he said, and, in particular, I was struck by his unusual use of the word "endure", which he definitely said.)
Interpretation: A person who receives as much anthrax in the mail as he did, with a warning letter, understands the implicit threat.