1. Elementary separation-of-powers principles ought to counsel strongly against a sitting judge’s sending a president a letter of advice on how to conduct American foreign policy. Given its general terms, it’s not surprising that the Code of Conduct for United States Judges (which, as Matt points out, doesn’t formally apply to Supreme Court justices) doesn’t speak directly to this question. But the significant limitations that the Code of Conduct places on a judge’s “consult[ing] with or appear[ing] at a public hearing before an executive or legislative body or official”—see Canon 4.A(2)—reflect those fundamental separation-of-powers principles.
2. Justice O’Connor is one of 14 signatories to the letter. Does anyone (herself included) really believe that she has any particular wisdom to provide on how President Obama ought to address the Israeli-Palestinian conflict? Does anyone imagine that she played any role in drafting or editing the letter? (I’d bet that she barely skimmed it.) Whatever persuasive force the letter has would be exactly the same if she hadn’t signed her name to it. So her signing the letter is essentially a political act in which she is throwing her weight in support of one approach to American foreign policy at the same time that she continues to sit on cases. (In using the term “political act,” I don’t mean to maintain that her conduct would necessarily qualify as “political activity” barred by Canon 5 of the Code of Conduct; the contours of that term are far from clear.)
3. Matt states that O’Connor “has taken ‘senior status,’ not full retirement from the bench, and still occasionally sits on circuit panels and adjudicates cases.” The italicized passage certainly captures O’Connor’s view of her own status. I’ll just highlight that I’ve argued that O’Connor may in fact have fully retired from her office in 2006 and, if so, that her sitting as a judge since then has been unlawful.